/* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
   Copyright (c) 2008, 2021, MariaDB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */

/*
  TODO:
  Fix that MAYBE_KEY are stored in the tree so that we can detect use
  of full hash keys for queries like:

  select s.id, kws.keyword_id from sites as s,kws where s.id=kws.site_id and
  kws.keyword_id in (204,205);
*/

/*
  This file contains:

  RangeAnalysisModule  
    A module that accepts a condition, index (or partitioning) description, 
    and builds lists of intervals (in index/partitioning space), such that 
    all possible records that match the condition are contained within the 
    intervals.
    The entry point for the range analysis module is get_mm_tree() function.
    
    The lists are returned in form of complicated structure of interlinked
    SEL_TREE/SEL_IMERGE/SEL_ARG objects.
    See quick_range_seq_next, find_used_partitions for examples of how to walk 
    this structure.
    All direct "users" of this module are located within this file, too.


  PartitionPruningModule
    A module that accepts a partitioned table, condition, and finds which
    partitions we will need to use in query execution. Search down for
    "PartitionPruningModule" for description.
    The module has single entry point - prune_partitions() function.


  Range/index_merge/groupby-minmax optimizer module  
    A module that accepts a table, condition, and returns 
     - a QUICK_*_SELECT object that can be used to retrieve rows that match
       the specified condition, or a "no records will match the condition" 
       statement.

    The module entry points are
      test_quick_select()
      get_quick_select_for_ref()


  Record retrieval code for range/index_merge/groupby-min-max.
    Implementations of QUICK_*_SELECT classes.

  KeyTupleFormat
  ~~~~~~~~~~~~~~
  The code in this file (and elsewhere) makes operations on key value tuples.
  Those tuples are stored in the following format:
  
  The tuple is a sequence of key part values. The length of key part value
  depends only on its type (and not depends on the what value is stored)
  
    KeyTuple: keypart1-data, keypart2-data, ...
  
  The value of each keypart is stored in the following format:
  
    keypart_data: [isnull_byte] keypart-value-bytes

  If a keypart may have a NULL value (key_part->field->real_maybe_null() can
  be used to check this), then the first byte is a NULL indicator with the 
  following valid values:
    1  - keypart has NULL value.
    0  - keypart has non-NULL value.

  <questionable-statement> If isnull_byte==1 (NULL value), then the following
  keypart->length bytes must be 0.
  </questionable-statement>

  keypart-value-bytes holds the value. Its format depends on the field type.
  The length of keypart-value-bytes may or may not depend on the value being
  stored. The default is that length is static and equal to 
  KEY_PART_INFO::length.
  
  Key parts with (key_part_flag & HA_BLOB_PART) have length depending of the 
  value:
  
     keypart-value-bytes: value_length value_bytes

  The value_length part itself occupies HA_KEY_BLOB_LENGTH=2 bytes.

  See key_copy() and key_restore() for code to move data between index tuple
  and table record

  CAUTION: the above description is only sergefp's understanding of the 
           subject and may omit some details.
*/

#include "mariadb.h"
#include "sql_priv.h"
#include "key.h"        // is_key_used, key_copy, key_cmp, key_restore
#include "sql_parse.h"                          // check_stack_overrun
#include "sql_partition.h"    // get_part_id_func, PARTITION_ITERATOR,
                              // struct partition_info, NOT_A_PARTITION_ID
#include "records.h"          // init_read_record, end_read_record
#include <m_ctype.h>
#include "sql_select.h"
#include "sql_statistics.h"
#include "uniques.h"
#include "my_json_writer.h"
#include "opt_hints.h"

#ifndef EXTRA_DEBUG
#define test_rb_tree(A,B) {}
#define test_use_count(A) {}
#endif

/*
  Convert double value to #rows. Currently this does floor(), and we
  might consider using round() instead.
*/
#define double2rows(x) ((ha_rows)(x))

/*
  this should be long enough so that any memcmp with a string that
  starts from '\0' won't cross is_null_string boundaries, even
  if the memcmp is optimized to compare 4- 8- or 16- bytes at once
*/
static uchar is_null_string[20]= {1,0};

/**
  Helper function to compare two SEL_ARG's.
*/
static bool all_same(const SEL_ARG *sa1, const SEL_ARG *sa2)
{
  if (sa1 == NULL && sa2 == NULL)
    return true;
  if ((sa1 != NULL && sa2 == NULL) || (sa1 == NULL && sa2 != NULL))
    return false;
  return sa1->all_same(sa2);
}

class SEL_IMERGE;

#define CLONE_KEY1_MAYBE 1
#define CLONE_KEY2_MAYBE 2
#define swap_clone_flag(A) ((A & 1) << 1) | ((A & 2) >> 1)


/*
  While objects of the class SEL_ARG represent ranges for indexes or
  index infixes (including ranges for index prefixes and index suffixes),
  objects of the class SEL_TREE represent AND/OR formulas of such ranges.
  Currently an AND/OR formula represented by a SEL_TREE object can have
  at most three levels: 

    <SEL_TREE formula> ::= 
      [ <SEL_RANGE_TREE formula> AND ]
      [ <SEL_IMERGE formula> [ AND <SEL_IMERGE formula> ...] ]

    <SEL_RANGE_TREE formula> ::=
      <SEL_ARG formula> [ AND  <SEL_ARG_formula> ... ]

    <SEL_IMERGE formula> ::=  
      <SEL_RANGE_TREE formula> [ OR <SEL_RANGE_TREE formula> ]

  As we can see from the above definitions:
   - SEL_RANGE_TREE formula is a conjunction of SEL_ARG formulas
   - SEL_IMERGE formula is a disjunction of SEL_RANGE_TREE formulas
   - SEL_TREE formula is a conjunction of a SEL_RANGE_TREE formula
     and SEL_IMERGE formulas. 
  It's required above that a SEL_TREE formula has at least one conjunct.

  Usually we will consider normalized SEL_RANGE_TREE formulas where we use
  TRUE as conjunct members for those indexes whose SEL_ARG trees are empty.
  
  We will call an SEL_TREE object simply 'tree'. 
  The part of a tree that represents SEL_RANGE_TREE formula is called
  'range part' of the tree while the remaining part is called 'imerge part'. 
  If a tree contains only a range part then we call such a tree 'range tree'.
  Components of a range tree that represent SEL_ARG formulas are called ranges.
  If a tree does not contain any range part we call such a tree 'imerge tree'.
  Components of the imerge part of a tree that represent SEL_IMERGE formula
  are called imerges.

  Usually we'll designate:
    SEL_TREE formulas         by T_1,...,T_k
    SEL_ARG formulas          by R_1,...,R_k
    SEL_RANGE_TREE formulas   by RT_1,...,RT_k
    SEL_IMERGE formulas       by M_1,...,M_k
  Accordingly we'll use:
    t_1,...,t_k - to designate trees representing T_1,...,T_k
    r_1,...,r_k - to designate ranges representing R_1,...,R_k 
    rt_1,...,r_tk - to designate range trees representing RT_1,...,RT_k
    m_1,...,m_k - to designate imerges representing M_1,...,M_k

  SEL_TREE objects are usually built from WHERE conditions or
  ON expressions.
  A SEL_TREE object always represents an inference of the condition it is
  built from. Therefore, if a row satisfies a SEL_TREE formula it also
  satisfies the condition it is built from.

  The following transformations of tree t representing SEL_TREE formula T 
  yield a new tree t1 thar represents an inference of T: T=>T1.  
    (1) remove any of SEL_ARG tree from the range part of t
    (2) remove any imerge from the tree t 
    (3) remove any of SEL_ARG tree from any range tree contained
        in any imerge of tree   
 
  Since the basic blocks of any SEL_TREE objects are ranges, SEL_TREE
  objects in many cases can be effectively used to filter out a big part
  of table rows that do not satisfy WHERE/IN conditions utilizing
  only single or multiple range index scans.

  A single range index scan is constructed for a range tree that contains
  only one SEL_ARG object for an index or an index prefix.
  An index intersection scan can be constructed for a range tree
  that contains several SEL_ARG objects. Currently index intersection
  scans are constructed only for single-point ranges.
  An index merge scan is constructed for a imerge tree that contains only
  one imerge. If range trees of this imerge contain only single-point merges
  than a union of index intersections can be built.

  Usually the tree built by the range optimizer for a query table contains
  more than one range in the range part, and additionally may contain some
  imerges in the imerge part. The range optimizer evaluates all of them one
  by one and chooses the range or the imerge that provides the cheapest
  single or multiple range index scan of the table.  According to rules 
  (1)-(3) this scan always filter out only those rows that do not satisfy
  the query conditions. 

  For any condition the SEL_TREE object for it is built in a bottom up
  manner starting from the range trees for the predicates. The tree_and
  function builds a tree for any conjunction of formulas from the trees
  for its conjuncts. The tree_or function builds a tree for any disjunction
  of formulas from the trees for its disjuncts.    
*/ 
  
class SEL_TREE :public Sql_alloc
{
public:
  /*
    Starting an effort to document this field:
    (for some i, keys[i]->type == SEL_ARG::IMPOSSIBLE) => 
       (type == SEL_TREE::IMPOSSIBLE)
  */
  enum Type { IMPOSSIBLE, ALWAYS, MAYBE, KEY, KEY_SMALLER } type;

  SEL_TREE(enum Type type_arg, MEM_ROOT *root, size_t num_keys)
    : type(type_arg), keys(root, num_keys), n_ror_scans(0)
  {
    keys_map.clear_all();
  }

  SEL_TREE(MEM_ROOT *root, size_t num_keys) :
    type(KEY), keys(root, num_keys), n_ror_scans(0)
  { 
    keys_map.clear_all();
  }
   
  SEL_TREE(SEL_TREE *arg, bool without_merges, RANGE_OPT_PARAM *param);
  /*
    Note: there may exist SEL_TREE objects with sel_tree->type=KEY and
    keys[i]=0 for all i. (SergeyP: it is not clear whether there is any
    merit in range analyzer functions (e.g. get_mm_parts) returning a
    pointer to such SEL_TREE instead of NULL)
  */
  Mem_root_array<SEL_ARG *, true> keys;
  key_map keys_map;        /* bitmask of non-NULL elements in keys */

  /*
    Possible ways to read rows using index_merge. The list is non-empty only
    if type==KEY. Currently can be non empty only if keys_map.is_clear_all().
  */
  List<SEL_IMERGE> merges;

  /* The members below are filled/used only after get_mm_tree is done */
  key_map ror_scans_map;   /* bitmask of ROR scan-able elements in keys */
  uint    n_ror_scans;     /* number of set bits in ror_scans_map */

  struct st_index_scan_info **index_scans;     /* list of index scans */
  struct st_index_scan_info **index_scans_end; /* last index scan */

  struct st_ror_scan_info **ror_scans;     /* list of ROR key scans */
  struct st_ror_scan_info **ror_scans_end; /* last ROR scan */
  /* Note that #records for each key scan is stored in table->quick_rows */

  bool without_ranges() { return keys_map.is_clear_all(); }
  bool without_imerges() { return merges.is_empty(); }
};


class PARAM : public RANGE_OPT_PARAM
{
public:
  ha_rows quick_rows[MAX_KEY];

  /*
    This will collect 'possible keys' based on the range optimization.
    
    Queries with a JOIN object actually use ref optimizer (see add_key_field)
    to collect possible_keys. This is used by single table UPDATE/DELETE.
  */
  key_map possible_keys;
  longlong baseflag;
  uint max_key_parts, range_count;

  bool quick;				// Don't calculate possible keys

  uint fields_bitmap_size;
  MY_BITMAP needed_fields;    /* bitmask of fields needed by the query */
  MY_BITMAP tmp_covered_fields;

  key_map *needed_reg;        /* ptr to SQL_SELECT::needed_reg */

  uint *imerge_cost_buff;     /* buffer for index_merge cost estimates */
  uint imerge_cost_buff_size; /* size of the buffer */

  /* Number of ranges in the last checked tree->key */
  uint n_ranges;
  uint8 first_null_comp; /* first null component if any, 0 - otherwise */
};


class TABLE_READ_PLAN;
  class TRP_RANGE;
  class TRP_ROR_INTERSECT;
  class TRP_ROR_UNION;
  class TRP_INDEX_INTERSECT;
  class TRP_INDEX_MERGE;
  class TRP_GROUP_MIN_MAX;

struct st_index_scan_info;
struct st_ror_scan_info;

static bool is_key_scan_ror(PARAM *param, uint keynr, uint8 nparts);
static ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
                                  bool index_only,
                                  SEL_ARG *tree, bool update_tbl_stats, 
                                  uint *mrr_flags, uint *bufsize,
                                  Cost_estimate *cost, bool *is_ror_scan);

QUICK_RANGE_SELECT *get_quick_select(PARAM *param,uint index,
                                     SEL_ARG *key_tree, uint mrr_flags, 
                                     uint mrr_buf_size, MEM_ROOT *alloc);
static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
                                       bool index_read_must_be_used,
                                       bool for_range_access,
                                       double read_time, ha_rows limit,
                                       bool using_table_scan);
static
TRP_INDEX_INTERSECT *get_best_index_intersect(PARAM *param, SEL_TREE *tree,
                                              double read_time);
static
TRP_ROR_INTERSECT *get_best_ror_intersect(const PARAM *param, SEL_TREE *tree,
                                          double read_time,
                                          bool *are_all_covering,
                                          bool force_index_merge_result);
static
TRP_ROR_INTERSECT *get_best_covering_ror_intersect(PARAM *param,
                                                   SEL_TREE *tree,
                                                   double read_time,
                                                   bool force_index_merge);
static
TABLE_READ_PLAN *get_best_disjunct_quick(PARAM *param,
                                         bool index_merge_union_allowed,
                                         bool index_merge_sort_union_allowed,
                                         SEL_IMERGE *imerge,
                                         double read_time,
                                         ha_rows limit,
                                         bool named_trace,
                                         bool using_table_scan);
static
TABLE_READ_PLAN *merge_same_index_scans(PARAM *param, SEL_IMERGE *imerge,
                                        TRP_INDEX_MERGE *imerge_trp,
                                        double read_time,
                                        bool index_merge_union_allowed,
                                        bool index_merge_sort_union_allowed);
static
TRP_GROUP_MIN_MAX *get_best_group_min_max(PARAM *param, SEL_TREE *tree,
                                          double read_time);

#ifndef DBUG_OFF
static void print_sel_tree(PARAM *param, SEL_TREE *tree, key_map *tree_map,
                           const char *msg);
static void print_ror_scans_arr(TABLE *table, const char *msg,
                                struct st_ror_scan_info **start,
                                struct st_ror_scan_info **end);
static void print_quick(QUICK_SELECT_I *quick, const key_map *needed_reg);
#endif

static SEL_TREE *tree_and(RANGE_OPT_PARAM *param,
                          SEL_TREE *tree1, SEL_TREE *tree2);
static SEL_TREE *tree_or(RANGE_OPT_PARAM *param,
                         SEL_TREE *tree1,SEL_TREE *tree2);
static SEL_ARG *sel_add(SEL_ARG *key1,SEL_ARG *key2);
static SEL_ARG *key_or(RANGE_OPT_PARAM *param,
                       SEL_ARG *key1, SEL_ARG *key2);
static SEL_ARG *key_and(RANGE_OPT_PARAM *param,
                        SEL_ARG *key1, SEL_ARG *key2,
                        uint clone_flag);
static SEL_ARG *key_or_with_limit(RANGE_OPT_PARAM *param, uint keyno,
                                  SEL_ARG *key1, SEL_ARG *key2);
static SEL_ARG *key_and_with_limit(RANGE_OPT_PARAM *param, uint keyno,
                                   SEL_ARG *key1, SEL_ARG *key2,
                                   uint clone_flag);
static bool get_range(SEL_ARG **e1,SEL_ARG **e2,SEL_ARG *root1);
bool get_quick_keys(PARAM *param,QUICK_RANGE_SELECT *quick,KEY_PART *key,
                    SEL_ARG *key_tree, uchar *min_key,uint min_key_flag,
                    uchar *max_key,uint max_key_flag);
static bool eq_tree(SEL_ARG* a,SEL_ARG *b);

SEL_ARG null_element(SEL_ARG::IMPOSSIBLE);
static bool null_part_in_key(KEY_PART *key_part, const uchar *key,
                             uint length);

static
SEL_ARG *enforce_sel_arg_weight_limit(RANGE_OPT_PARAM *param, uint keyno,
                                      SEL_ARG *sel_arg);
static
bool sel_arg_and_weight_heuristic(RANGE_OPT_PARAM *param, SEL_ARG *key1,
                                  SEL_ARG *key2);

#include "opt_range_mrr.cc"

static bool sel_trees_have_common_keys(SEL_TREE *tree1, SEL_TREE *tree2, 
                                       key_map *common_keys);
static void eliminate_single_tree_imerges(RANGE_OPT_PARAM *param,
                                          SEL_TREE *tree);

static bool sel_trees_can_be_ored(RANGE_OPT_PARAM* param,
                                  SEL_TREE *tree1, SEL_TREE *tree2, 
                                  key_map *common_keys);
static bool sel_trees_must_be_ored(RANGE_OPT_PARAM* param,
                                   SEL_TREE *tree1, SEL_TREE *tree2,
                                   key_map common_keys);
static int and_range_trees(RANGE_OPT_PARAM *param,
                           SEL_TREE *tree1, SEL_TREE *tree2,
                           SEL_TREE *result);
static bool remove_nonrange_trees(PARAM *param, SEL_TREE *tree);
static void restore_nonrange_trees(RANGE_OPT_PARAM *param, SEL_TREE *tree,
                                   SEL_ARG **backup);
static void print_key_value(String *out, const KEY_PART_INFO *key_part,
                            const uchar* key, uint length);
static void print_keyparts_name(String *out, const KEY_PART_INFO *key_part,
                                uint n_keypart, key_part_map keypart_map);

static void trace_ranges(Json_writer_array *range_trace,
                         PARAM *param, uint idx,
                         SEL_ARG *keypart,
                         const KEY_PART_INFO *key_parts);

static
void print_range(String *out, const KEY_PART_INFO *key_part,
                 KEY_MULTI_RANGE *range, uint n_key_parts);

static
void print_range_for_non_indexed_field(String *out, Field *field,
                                       KEY_MULTI_RANGE *range);

static void print_min_range_operator(String *out, const ha_rkey_function flag);
static void print_max_range_operator(String *out, const ha_rkey_function flag);

static bool is_field_an_unique_index(Field *field);

/*
  SEL_IMERGE is a list of possible ways to do index merge, i.e. it is
  a condition in the following form:
   (t_1||t_2||...||t_N) && (next)

  where all t_i are SEL_TREEs, next is another SEL_IMERGE and no pair
  (t_i,t_j) contains SEL_ARGS for the same index.

  SEL_TREE contained in SEL_IMERGE always has merges=NULL.

  This class relies on memory manager to do the cleanup.
*/

class SEL_IMERGE : public Sql_alloc
{
  enum { PREALLOCED_TREES= 10};
public:
  SEL_TREE *trees_prealloced[PREALLOCED_TREES];
  SEL_TREE **trees;             /* trees used to do index_merge   */
  SEL_TREE **trees_next;        /* last of these trees            */
  SEL_TREE **trees_end;         /* end of allocated space         */

  SEL_ARG  ***best_keys;        /* best keys to read in SEL_TREEs */

  SEL_IMERGE() :
    trees(&trees_prealloced[0]),
    trees_next(trees),
    trees_end(trees + PREALLOCED_TREES)
  {}
  SEL_IMERGE (SEL_IMERGE *arg, uint cnt, RANGE_OPT_PARAM *param);
  int or_sel_tree(RANGE_OPT_PARAM *param, SEL_TREE *tree);
  bool have_common_keys(RANGE_OPT_PARAM *param, SEL_TREE *tree);
  int and_sel_tree(RANGE_OPT_PARAM *param, SEL_TREE *tree, 
                   SEL_IMERGE *new_imerge);
  int or_sel_tree_with_checks(RANGE_OPT_PARAM *param,
                              uint n_init_trees, 
                              SEL_TREE *new_tree,
                              bool is_first_check_pass,
                              bool *is_last_check_pass);
  int or_sel_imerge_with_checks(RANGE_OPT_PARAM *param,
                                uint n_init_trees,
                                SEL_IMERGE* imerge,
                                bool is_first_check_pass,
                                bool *is_last_check_pass);
};


/*
  Add a range tree to the range trees of this imerge 

  SYNOPSIS
    or_sel_tree()
      param                  Context info for the operation         
      tree                   SEL_TREE to add to this imerge 

  DESCRIPTION 
    The function just adds the range tree 'tree' to the range trees
    of this imerge.

  RETURN
     0   if the operation is success
    -1   if the function runs out memory
*/

int SEL_IMERGE::or_sel_tree(RANGE_OPT_PARAM *param, SEL_TREE *tree)
{
  if (trees_next == trees_end)
  {
    const int realloc_ratio= 2;		/* Double size for next round */
    size_t old_elements= (trees_end - trees);
    size_t old_size= sizeof(SEL_TREE**) * old_elements;
    size_t new_size= old_size * realloc_ratio;
    SEL_TREE **new_trees;
    if (!(new_trees= (SEL_TREE**)alloc_root(param->mem_root, new_size)))
      return -1;
    memcpy(new_trees, trees, old_size);
    trees=      new_trees;
    trees_next= trees + old_elements;
    trees_end=  trees + old_elements * realloc_ratio;
  }
  *(trees_next++)= tree;
  return 0;
}


/*
  Check if any of the range trees of this imerge intersects with a given tree 

  SYNOPSIS
    have_common_keys()
      param    Context info for the function
      tree     SEL_TREE intersection with the imerge range trees is checked for 

  DESCRIPTION
    The function checks whether there is any range tree rt_i in this imerge
    such that there are some indexes for which ranges are defined in both
    rt_i and the range part of the SEL_TREE tree.  
    To check this the function calls the function sel_trees_have_common_keys.

  RETURN 
    TRUE    if there are such range trees in this imerge
    FALSE   otherwise
*/

bool SEL_IMERGE::have_common_keys(RANGE_OPT_PARAM *param, SEL_TREE *tree)
{
  for (SEL_TREE** or_tree= trees, **bound= trees_next;
       or_tree != bound; or_tree++)
  {
    key_map common_keys;
    if (sel_trees_have_common_keys(*or_tree, tree, &common_keys))
      return TRUE;
  }
  return FALSE;
}


/* 
  Perform AND operation for this imerge and the range part of a tree

  SYNOPSIS
    and_sel_tree()
      param           Context info for the operation
      tree            SEL_TREE for the second operand of the operation
      new_imerge  OUT imerge for the result of the operation

  DESCRIPTION
    This function performs AND operation for this imerge m and the
    range part of the SEL_TREE tree rt. In other words the function
    pushes rt into this imerge. The resulting imerge is returned in
    the parameter new_imerge.
    If this imerge m represent the formula
      RT_1 OR ... OR RT_k
    then the resulting imerge of the function represents the formula
      (RT_1 AND RT) OR ... OR (RT_k AND RT)
    The function calls the function and_range_trees to construct the
    range tree representing (RT_i AND RT).
    
  NOTE
    The function may return an empty imerge without any range trees.
    This happens when each call of and_range_trees returns an 
    impossible range tree (SEL_TREE::IMPOSSIBLE).
    Example: (key1 < 2 AND key2 > 10) AND (key1 > 4 OR key2 < 6).
         
  RETURN
     0  if the operation is a success
    -1  otherwise: there is not enough memory to perform the operation
*/

int SEL_IMERGE::and_sel_tree(RANGE_OPT_PARAM *param, SEL_TREE *tree,
                             SEL_IMERGE *new_imerge)
{
  for (SEL_TREE** or_tree= trees; or_tree != trees_next; or_tree++) 
  {
    SEL_TREE *res_or_tree= 0;
    SEL_TREE *and_tree= 0;
    if (!(res_or_tree= new SEL_TREE(param->mem_root, param->keys)) ||
        !(and_tree= new SEL_TREE(tree, TRUE, param)))
      return (-1);
    if (!and_range_trees(param, *or_tree, and_tree, res_or_tree))
    {
      if (new_imerge->or_sel_tree(param, res_or_tree))
        return (-1);
    }        
  }
  return 0;
}      


/*
  Perform OR operation on this imerge and the range part of a tree

  SYNOPSIS
    or_sel_tree_with_checks()
      param                  Context info for the operation 
      n_trees                Number of trees in this imerge to check for oring        
      tree                   SEL_TREE whose range part is to be ored 
      is_first_check_pass    <=> the first call of the function for this imerge  
      is_last_check_pass OUT <=> no more calls of the function for this imerge

  DESCRIPTION
    The function performs OR operation on this imerge m and the range part
    of the SEL_TREE tree rt. It always replaces this imerge with the result
    of the operation.
 
    The operation can be performed in two different modes: with
    is_first_check_pass==TRUE and is_first_check_pass==FALSE, transforming
    this imerge differently.

    Given this imerge represents the formula
      RT_1 OR ... OR RT_k:

    1. In the first mode, when is_first_check_pass==TRUE :
      1.1. If rt must be ored(see the function sel_trees_must_be_ored) with
           some rt_j (there may be only one such range tree in the imerge)
           then the function produces an imerge representing the formula
             RT_1 OR ... OR (RT_j OR RT) OR ... OR RT_k,
           where the tree for (RT_j OR RT) is built by oring the pairs
           of SEL_ARG trees for the corresponding indexes
      1.2. Otherwise the function produces the imerge representing the formula:
           RT_1 OR ... OR RT_k OR RT.

    2. In the second mode, when is_first_check_pass==FALSE :
      2.1. For each rt_j in the imerge that can be ored (see the function
           sel_trees_can_be_ored) with rt the function replaces rt_j for a
           range tree such that for each index for which ranges are defined
           in both in rt_j and rt  the tree contains the  result of oring of
           these ranges.
      2.2. In other cases the function does not produce any imerge.

    When is_first_check==TRUE the function returns FALSE in the parameter
    is_last_check_pass if there is no rt_j such that rt_j can be ored with rt,
    but, at the same time, it's not true that rt_j must be ored with rt.
    When is_first_check==FALSE the function always returns FALSE in the
    parameter is_last_check_pass.    
          
  RETURN
    1  The result of oring of rt_j and rt that must be ored returns the
       the range tree with type==SEL_TREE::ALWAYS
       (in this case the imerge m should be discarded)
   -1  The function runs out of memory
    0  in all other cases 
*/

int SEL_IMERGE::or_sel_tree_with_checks(RANGE_OPT_PARAM *param,
                                        uint n_trees,
                                        SEL_TREE *tree,
                                        bool is_first_check_pass,
                                        bool *is_last_check_pass)
{
  bool was_ored= FALSE;
  *is_last_check_pass= is_first_check_pass;
  SEL_TREE** or_tree= trees;
  for (uint i= 0; i < n_trees; i++, or_tree++)
  {
    SEL_TREE *result= 0;
    key_map result_keys;
    key_map ored_keys;
    if (sel_trees_can_be_ored(param, *or_tree, tree, &ored_keys))
    {
      bool must_be_ored= sel_trees_must_be_ored(param, *or_tree, tree,
                                                ored_keys);
      if (must_be_ored || !is_first_check_pass)
      {
        result_keys.clear_all();
        result= *or_tree;
        for (uint key_no= 0; key_no < param->keys; key_no++)
        {
          if (!ored_keys.is_set(key_no))
	  {
            result->keys[key_no]= 0;
	    continue;
          }
          SEL_ARG *key1= (*or_tree)->keys[key_no];
          SEL_ARG *key2= tree->keys[key_no];
          key2->incr_refs();
          if ((result->keys[key_no]= key_or_with_limit(param, key_no, key1,
                                                       key2)))
          {
            
            result_keys.set_bit(key_no);
#ifdef EXTRA_DEBUG
            if (param->alloced_sel_args <
                param->thd->variables.optimizer_max_sel_args)
	    {
              key1= result->keys[key_no]; 
              (key1)->test_use_count(key1);
            }
#endif
          }       
        }
      }
      else if(is_first_check_pass) 
        *is_last_check_pass= FALSE;
    } 

    if (result)
    {
      result->keys_map= result_keys;
      if (result_keys.is_clear_all())
        result->type= SEL_TREE::ALWAYS;
      if ((result->type == SEL_TREE::MAYBE) ||
          (result->type == SEL_TREE::ALWAYS))
        return 1;
      /* SEL_TREE::IMPOSSIBLE is impossible here */
      *or_tree= result;
      was_ored= TRUE;
    }
  }
  if (was_ored)
    return 0;

  if (is_first_check_pass && !*is_last_check_pass &&
      !(tree= new SEL_TREE(tree, FALSE, param)))
    return (-1);
  return or_sel_tree(param, tree);
}


/*
  Perform OR operation on this imerge and and another imerge

  SYNOPSIS
    or_sel_imerge_with_checks()
      param                  Context info for the operation 
      n_trees           Number of trees in this imerge to check for oring        
      imerge                 The second operand of the operation 
      is_first_check_pass    <=> the first call of the function for this imerge  
      is_last_check_pass OUT <=> no more calls of the function for this imerge

  DESCRIPTION
    For each range tree rt from 'imerge' the function calls the method
    SEL_IMERGE::or_sel_tree_with_checks that performs OR operation on this
    SEL_IMERGE object m and the tree rt. The mode of the operation is
    specified by the parameter is_first_check_pass. Each call of
    SEL_IMERGE::or_sel_tree_with_checks transforms this SEL_IMERGE object m.
    The function returns FALSE in the prameter is_last_check_pass if
    at least one of the calls of SEL_IMERGE::or_sel_tree_with_checks
    returns FALSE as the value of its last parameter. 
    
  RETURN
    1  One of the calls of SEL_IMERGE::or_sel_tree_with_checks returns 1.
       (in this case the imerge m should be discarded)
   -1  The function runs out of memory
    0  in all other cases 
*/

int SEL_IMERGE::or_sel_imerge_with_checks(RANGE_OPT_PARAM *param,
                                          uint n_trees,
                                          SEL_IMERGE* imerge,
                                          bool is_first_check_pass,
                                          bool *is_last_check_pass)
{
  *is_last_check_pass= TRUE;
  SEL_TREE** tree= imerge->trees;
  SEL_TREE** tree_end= imerge->trees_next;
  for ( ; tree < tree_end; tree++)
  {
    uint rc;
    bool is_last= TRUE; 
    rc= or_sel_tree_with_checks(param, n_trees, *tree, 
                               is_first_check_pass, &is_last);
    if (!is_last)
      *is_last_check_pass= FALSE;
    if (rc)
      return rc;
  }
  return 0;
}


/*
  Copy constructor for SEL_TREE objects

  SYNOPSIS
    SEL_TREE
      arg            The source tree for the constructor
      without_merges <=> only the range part of the tree arg is copied
      param          Context info for the operation

  DESCRIPTION
    The constructor creates a full copy of the SEL_TREE arg if
    the prameter without_merges==FALSE. Otherwise a tree is created
    that contains the copy only of the range part of the tree arg. 
*/ 

SEL_TREE::SEL_TREE(SEL_TREE *arg, bool without_merges,
                   RANGE_OPT_PARAM *param) 
  : Sql_alloc(),
    keys(param->mem_root, param->keys),
    n_ror_scans(0)
{
  keys_map= arg->keys_map;
  type= arg->type;
  MEM_ROOT *mem_root;

  for (uint idx= 0; idx < param->keys; idx++)
  {
    if ((keys[idx]= arg->keys[idx]))
      keys[idx]->incr_refs_all();
  }

  if (without_merges)
    return;

  mem_root= current_thd->mem_root;
  List_iterator<SEL_IMERGE> it(arg->merges);
  for (SEL_IMERGE *el= it++; el; el= it++)
  {
    SEL_IMERGE *merge= new (mem_root) SEL_IMERGE(el, 0, param);
    if (!merge || merge->trees == merge->trees_next)
    {
      merges.empty();
      return;
    }
    merges.push_back(merge, mem_root);
  }
}


/*
  Copy constructor for SEL_IMERGE objects

  SYNOPSIS
    SEL_IMERGE
      arg         The source imerge for the constructor
      cnt         How many trees from arg are to be copied
      param       Context info for the operation

  DESCRIPTION
    The cnt==0 then the constructor creates a full copy of the 
    imerge arg. Otherwise only the first cnt trees of the imerge
    are copied.
*/ 

SEL_IMERGE::SEL_IMERGE(SEL_IMERGE *arg, uint cnt,
                       RANGE_OPT_PARAM *param) : Sql_alloc()
{
  size_t elements= (arg->trees_end - arg->trees);
  if (elements > PREALLOCED_TREES)
  {
    size_t size= elements * sizeof (SEL_TREE **);
    if (!(trees= (SEL_TREE **)alloc_root(param->mem_root, size)))
      goto mem_err;
  }
  else
    trees= &trees_prealloced[0];

  trees_next= trees + (cnt ? cnt : arg->trees_next-arg->trees);
  trees_end= trees + elements;

  for (SEL_TREE **tree= trees, **arg_tree= arg->trees; tree < trees_next;
       tree++, arg_tree++)
  {
    if (!(*tree= new SEL_TREE(*arg_tree, TRUE, param)))
      goto mem_err;
  }

  return;

mem_err:
  trees= &trees_prealloced[0];
  trees_next= trees;
  trees_end= trees;
}


/*
  Perform AND operation on two imerge lists

  SYNOPSIS
    imerge_list_and_list()
      param             Context info for the operation         
      im1               The first imerge list for the operation
      im2               The second imerge list for the operation

  DESCRIPTION
    The function just appends the imerge list im2 to the imerge list im1  
    
  RETURN VALUE
    none
*/

inline void imerge_list_and_list(List<SEL_IMERGE> *im1, List<SEL_IMERGE> *im2)
{
  im1->append(im2);
}


/*
  Perform OR operation on two imerge lists

  SYNOPSIS
    imerge_list_or_list()
      param             Context info for the operation         
      im1               The first imerge list for the operation
      im2               The second imerge list for the operation
     
  DESCRIPTION
    Assuming that the first imerge list represents the formula
      F1= M1_1 AND ... AND M1_k1 
    while the second imerge list represents the formula 
      F2= M2_1 AND ... AND M2_k2,
    where M1_i= RT1_i_1 OR ... OR RT1_i_l1i (i in [1..k1])
    and M2_i = RT2_i_1 OR ... OR RT2_i_l2i (i in [1..k2]),
    the function builds a list of imerges for some formula that can be 
    inferred from the formula (F1 OR F2).

    More exactly the function builds imerges for the formula (M1_1 OR M2_1).
    Note that
      (F1 OR F2) = (M1_1 AND ... AND M1_k1) OR (M2_1 AND ... AND M2_k2) =
      AND (M1_i OR M2_j) (i in [1..k1], j in [1..k2]) =>
      M1_1 OR M2_1.
    So (M1_1 OR M2_1) is indeed an inference formula for (F1 OR F2).

    To build imerges for the formula (M1_1 OR M2_1) the function invokes,
    possibly twice, the method SEL_IMERGE::or_sel_imerge_with_checks
    for the imerge m1_1.
    At its first invocation the method SEL_IMERGE::or_sel_imerge_with_checks
    performs OR operation on the imerge m1_1 and the range tree rt2_1_1 by
    calling SEL_IMERGE::or_sel_tree_with_checks with is_first_pass_check==TRUE.
    The resulting imerge of the operation is ored with the next range tree of
    the imerge m2_1. This oring continues until the last range tree from
    m2_1 has been ored. 
    At its second invocation the method SEL_IMERGE::or_sel_imerge_with_checks
    performs the same sequence of OR operations, but now calling
    SEL_IMERGE::or_sel_tree_with_checks with is_first_pass_check==FALSE.

    The imerges that the operation produces replace those in the list im1   
       
  RETURN
    0     if the operation is a success 
   -1     if the function has run out of memory 
*/

int imerge_list_or_list(RANGE_OPT_PARAM *param,
                        List<SEL_IMERGE> *im1,
                        List<SEL_IMERGE> *im2)
{

  uint rc;
  bool is_last_check_pass= FALSE;
  SEL_IMERGE *imerge= im1->head();
  uint elems= (uint)(imerge->trees_next-imerge->trees);
  MEM_ROOT *mem_root= current_thd->mem_root;

  im1->empty();
  im1->push_back(imerge, mem_root);

  rc= imerge->or_sel_imerge_with_checks(param, elems, im2->head(),
                                        TRUE, &is_last_check_pass);
  if (rc)
  {
    if (rc == 1)
    {
      im1->empty();
      rc= 0;
    }
    return rc;
  }

  if (!is_last_check_pass)
  {
    SEL_IMERGE* new_imerge= new (mem_root) SEL_IMERGE(imerge, elems, param);
    if (new_imerge)
    {
      is_last_check_pass= TRUE;
      rc= new_imerge->or_sel_imerge_with_checks(param, elems, im2->head(),
                                                 FALSE, &is_last_check_pass);
      if (!rc)
        im1->push_back(new_imerge, mem_root); 
    }
  }
  return rc;  
}


/*
  Perform OR operation for each imerge from a list and the range part of a tree

  SYNOPSIS
    imerge_list_or_tree()
      param       Context info for the operation
      merges      The list of imerges to be ored with the range part of tree          
      tree        SEL_TREE whose range part is to be ored with the imerges

  DESCRIPTION
    For each imerge mi from the list 'merges' the function performs OR
    operation with mi and the range part of 'tree' rt, producing one or
    two imerges.

    Given the merge mi represent the formula RTi_1 OR ... OR RTi_k, 
    the function forms the merges by the following rules:
 
    1. If rt cannot be ored with any of the trees rti the function just
       produces an imerge that represents the formula
         RTi_1 OR ... RTi_k OR RT.
    2. If there exist a tree rtj that must be ored with rt the function
       produces an imerge the represents the formula
         RTi_1 OR ... OR (RTi_j OR RT) OR ... OR RTi_k,
       where the range tree for (RTi_j OR RT) is constructed by oring the
       SEL_ARG trees that must be ored.
    3. For each rti_j that can be ored with rt the function produces
       the new tree rti_j' and substitutes rti_j for this new range tree.

    In any case the function removes mi from the list and then adds all
    produced imerges.

    To build imerges by rules 1-3 the function calls the method
    SEL_IMERGE::or_sel_tree_with_checks, possibly twice. With the first
    call it passes TRUE for the third parameter of the function.
    At this first call imerges by rules 1-2 are built. If the call
    returns FALSE as the return value of its fourth parameter then the
    function are called for the second time. At this call the imerge
    of rule 3 is produced.

    If a call of SEL_IMERGE::or_sel_tree_with_checks returns 1 then
    then it means that the produced tree contains an always true
    range tree and the whole imerge can be discarded.
    
  RETURN
    1     if no imerges are produced
    0     otherwise
*/

static
int imerge_list_or_tree(RANGE_OPT_PARAM *param,
                        List<SEL_IMERGE> *merges,
                        SEL_TREE *tree)
{
  SEL_IMERGE *imerge;
  List<SEL_IMERGE> additional_merges;
  List_iterator<SEL_IMERGE> it(*merges);
  MEM_ROOT *mem_root= current_thd->mem_root;
  
  while ((imerge= it++))
  {
    bool is_last_check_pass;
    int rc= 0;
    int rc1= 0;
    SEL_TREE *or_tree= new (mem_root) SEL_TREE (tree, FALSE, param);
    if (or_tree)
    {
      uint elems= (uint)(imerge->trees_next-imerge->trees);
      rc= imerge->or_sel_tree_with_checks(param, elems, or_tree,
                                          TRUE, &is_last_check_pass);
      if (!is_last_check_pass)
      {
        SEL_IMERGE *new_imerge= new (mem_root) SEL_IMERGE(imerge, elems,
                                                          param);
        if (new_imerge)
	{ 
          rc1= new_imerge->or_sel_tree_with_checks(param, elems, or_tree,
                                                   FALSE, &is_last_check_pass);
          if (!rc1)
            additional_merges.push_back(new_imerge, mem_root);
        }
      }
    }
    if (rc || rc1 || !or_tree)
      it.remove();
  }

  merges->append(&additional_merges);
  return merges->is_empty();
}


/*
  Perform pushdown operation of the range part of a tree into given imerges 

  SYNOPSIS
    imerge_list_and_tree()
      param           Context info for the operation
      merges   IN/OUT List of imerges to push the range part of 'tree' into
      tree            SEL_TREE whose range part is to be pushed into imerges
      replace         if the pushdow operation for a imerge is a success
                      then the original imerge is replaced for the result
                      of the pushdown 

  DESCRIPTION
    For each imerge from the list merges the function pushes the range part
    rt of 'tree' into the imerge. 
    More exactly if the imerge mi from the list represents the formula
      RTi_1 OR ... OR RTi_k 
    the function bulds a new imerge that represents the formula
      (RTi_1 AND RT) OR ... OR (RTi_k AND RT)
    and adds this imerge to the list merges.
    To perform this pushdown operation the function calls the method
    SEL_IMERGE::and_sel_tree. 
    For any imerge mi the new imerge is not created if for each pair of
    trees rti_j and rt the intersection of the indexes with defined ranges
    is empty.
    If the result of the pushdown operation for the imerge mi returns an
    imerge with no trees then then not only nothing is added to the list 
    merges but mi itself is removed from the list. 

  TODO
    Optimize the code in order to not create new SEL_IMERGE and new SER_TREE
    objects when 'replace' is TRUE. (Currently this function is called always
    with this parameter equal to TRUE.)
    
  RETURN
    1    if no imerges are left in the list merges             
    0    otherwise
*/

static
int imerge_list_and_tree(RANGE_OPT_PARAM *param,
                         List<SEL_IMERGE> *merges,
                         SEL_TREE *tree, 
                         bool replace)
{
  SEL_IMERGE *imerge;
  SEL_IMERGE *new_imerge= NULL;
  List<SEL_IMERGE> new_merges;
  List_iterator<SEL_IMERGE> it(*merges);
  MEM_ROOT *mem_root= current_thd->mem_root;
  
  while ((imerge= it++))
  {
    if (!new_imerge)
      new_imerge= new (mem_root) SEL_IMERGE();
    if (imerge->have_common_keys(param, tree) && 
        new_imerge && !imerge->and_sel_tree(param, tree, new_imerge))
    {
      if (new_imerge->trees == new_imerge->trees_next)
        it.remove();
      else
      { 
        if (replace)
          it.replace(new_imerge);
        else        
          new_merges.push_back(new_imerge, mem_root);
        new_imerge= NULL;
      }
    }
  }
  imerge_list_and_list(&new_merges, merges);
  *merges= new_merges;
  return merges->is_empty();
}


/***************************************************************************
** Basic functions for SQL_SELECT and QUICK_RANGE_SELECT
***************************************************************************/

	/* make a select from mysql info
	   Error is set as following:
	   0 = ok
	   1 = Got some error (out of memory?)
	   */

SQL_SELECT *make_select(TABLE *head, table_map const_tables,
			table_map read_tables, COND *conds,
                        SORT_INFO *filesort,
                        bool allow_null_cond,
                        int *error)
{
  SQL_SELECT *select;
  DBUG_ENTER("make_select");

  *error=0;

  if (!conds && !allow_null_cond)
    DBUG_RETURN(0);
  if (!(select= new (head->in_use->mem_root) SQL_SELECT))
  {
    *error= 1;			// out of memory
    DBUG_RETURN(0);		/* purecov: inspected */
  }
  select->read_tables=read_tables;
  select->const_tables=const_tables;
  select->head=head;
  select->cond= conds;

  if (filesort && my_b_inited(&filesort->io_cache))
  {
    /*
      Hijack the filesort io_cache for make_select
      SQL_SELECT will be responsible for ensuring that it's properly freed.
    */
    select->file= filesort->io_cache;
    select->records=(ha_rows) (select->file.end_of_file/
			       head->file->ref_length);
    my_b_clear(&filesort->io_cache);
  }
  DBUG_RETURN(select);
}


SQL_SELECT::SQL_SELECT() :quick(0),cond(0),pre_idx_push_select_cond(NULL),free_cond(0)
{
  quick_keys.clear_all(); needed_reg.clear_all();
  my_b_clear(&file);
}


void SQL_SELECT::cleanup()
{
  delete quick;
  quick= 0;
  if (free_cond)
  {
    free_cond=0;
    delete cond;
    cond= 0;
  }
  close_cached_file(&file);
}


SQL_SELECT::~SQL_SELECT()
{
  cleanup();
}

#undef index					// Fix for Unixware 7

QUICK_SELECT_I::QUICK_SELECT_I()
  :max_used_key_length(0),
   used_key_parts(0)
{}

QUICK_RANGE_SELECT::QUICK_RANGE_SELECT(THD *thd, TABLE *table, uint key_nr,
                                       bool no_alloc, MEM_ROOT *parent_alloc,
                                       bool *create_error)
  :thd(thd), no_alloc(no_alloc), parent_alloc(parent_alloc),
   free_file(0),cur_range(NULL),last_range(0),dont_free(0)
{
  my_bitmap_map *bitmap;
  DBUG_ENTER("QUICK_RANGE_SELECT::QUICK_RANGE_SELECT");

  in_ror_merged_scan= 0;
  index= key_nr;
  head=  table;
  key_part_info= head->key_info[index].key_part;

  /* 'thd' is not accessible in QUICK_RANGE_SELECT::reset(). */
  mrr_buf_size= thd->variables.mrr_buff_size;
  mrr_buf_desc= NULL;

  if (!no_alloc && !parent_alloc)
  {
    // Allocates everything through the internal memroot
    init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                   thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
    thd->mem_root= &alloc;
  }
  else
    bzero((char*) &alloc,sizeof(alloc));
  file= head->file;
  record= head->record[0];

  my_init_dynamic_array2(PSI_INSTRUMENT_ME, &ranges, sizeof(QUICK_RANGE*),
                         thd->alloc<QUICK_RANGE>(16), 16, 16,
                         MYF(MY_THREAD_SPECIFIC));

  /* Allocate a bitmap for used columns */
  if (!(bitmap= (my_bitmap_map*) thd->alloc(head->s->column_bitmap_size)))
  {
    column_bitmap.bitmap= 0;
    *create_error= 1;
  }
  else
    my_bitmap_init(&column_bitmap, bitmap, head->s->fields);
  DBUG_VOID_RETURN;
}


void QUICK_RANGE_SELECT::need_sorted_output()
{
  if (!(mrr_flags & HA_MRR_SORTED))
  {
    /*
      Native implementation can't produce sorted output. We'll have to
      switch to default
    */
    mrr_flags |= HA_MRR_USE_DEFAULT_IMPL; 
  }
  mrr_flags |= HA_MRR_SORTED;
}


int QUICK_RANGE_SELECT::init()
{
  DBUG_ENTER("QUICK_RANGE_SELECT::init");

  if (file->inited != handler::NONE)
    file->ha_index_or_rnd_end();
  DBUG_RETURN(FALSE);
}


void QUICK_RANGE_SELECT::range_end()
{
  if (file->inited != handler::NONE)
    file->ha_index_or_rnd_end();
}


QUICK_RANGE_SELECT::~QUICK_RANGE_SELECT()
{
  DBUG_ENTER("QUICK_RANGE_SELECT::~QUICK_RANGE_SELECT");
  if (!dont_free)
  {
    /* file is NULL for CPK scan on covering ROR-intersection */
    if (file) 
    {
      range_end();
      file->ha_end_keyread();
      if (free_file)
      {
        DBUG_PRINT("info", ("Freeing separate handler %p (free: %d)", file,
                            free_file));
        file->ha_external_unlock(current_thd);
        file->ha_close();
        delete file;
      }
    }
    delete_dynamic(&ranges); /* ranges are allocated in alloc */
    free_root(&alloc,MYF(0));
  }
  my_free(mrr_buf_desc);
  DBUG_VOID_RETURN;
}

/*
  QUICK_INDEX_SORT_SELECT works as follows:
  - Do index scans, accumulate rowids in the Unique object 
    (Unique will also sort and de-duplicate rowids)
  - Use rowids from unique to run a disk-ordered sweep
*/

QUICK_INDEX_SORT_SELECT::QUICK_INDEX_SORT_SELECT(THD *thd_param, TABLE *table)
  :unique(NULL), pk_quick_select(NULL), thd(thd_param)
{
  DBUG_ENTER("QUICK_INDEX_SORT_SELECT::QUICK_INDEX_SORT_SELECT");
  index= MAX_KEY;
  head= table;
  init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                 thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
  DBUG_VOID_RETURN;
}

int QUICK_INDEX_SORT_SELECT::init()
{
  DBUG_ENTER("QUICK_INDEX_SORT_SELECT::init");
  DBUG_RETURN(0);
}

int QUICK_INDEX_SORT_SELECT::reset()
{
  DBUG_ENTER("QUICK_INDEX_SORT_SELECT::reset");
  const int retval= read_keys_and_merge();
  DBUG_RETURN(retval);
}

bool
QUICK_INDEX_SORT_SELECT::push_quick_back(QUICK_RANGE_SELECT *quick_sel_range)
{
  DBUG_ENTER("QUICK_INDEX_SORT_SELECT::push_quick_back");
  if (head->file->is_clustering_key(quick_sel_range->index))
  {
   /*
     A quick_select over a clustered primary key is handled specifically
     Here we assume:
     - PK columns are included in any other merged index
     - Scan on the PK is disk-ordered.
       (not meeting #2 will only cause performance degradation)

       We could treat clustered PK as any other index, but that would
       be inefficient. There is no point in doing scan on
       CPK, remembering the rowid, then making rnd_pos() call with
       that rowid.
    */
    pk_quick_select= quick_sel_range;
    DBUG_RETURN(0);
  }
  DBUG_RETURN(quick_selects.push_back(quick_sel_range, thd->mem_root));
}

QUICK_INDEX_SORT_SELECT::~QUICK_INDEX_SORT_SELECT()
{
  List_iterator_fast<QUICK_RANGE_SELECT> quick_it(quick_selects);
  QUICK_RANGE_SELECT* quick;
  DBUG_ENTER("QUICK_INDEX_SORT_SELECT::~QUICK_INDEX_SORT_SELECT");
  delete unique;
  quick_it.rewind();
  while ((quick= quick_it++))
    quick->file= NULL;
  quick_selects.delete_elements();
  delete pk_quick_select;
  /* It's ok to call the next two even if they are already deinitialized */
  end_read_record(&read_record);
  free_root(&alloc,MYF(0));
  DBUG_VOID_RETURN;
}

QUICK_ROR_INTERSECT_SELECT::QUICK_ROR_INTERSECT_SELECT(THD *thd_param,
                                                       TABLE *table,
                                                       bool retrieve_full_rows,
                                                       MEM_ROOT *parent_alloc)
  : cpk_quick(NULL), thd(thd_param), need_to_fetch_row(retrieve_full_rows),
    scans_inited(FALSE)
{
  index= MAX_KEY;
  head= table;
  record= head->record[0];
  if (!parent_alloc)
    init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                   thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
  else
    bzero(&alloc, sizeof(MEM_ROOT));
  last_rowid= (uchar*) alloc_root(parent_alloc? parent_alloc : &alloc,
                                  head->file->ref_length);
}


/*
  Do post-constructor initialization.
  SYNOPSIS
    QUICK_ROR_INTERSECT_SELECT::init()

  RETURN
    0      OK
    other  Error code
*/

int QUICK_ROR_INTERSECT_SELECT::init()
{
  DBUG_ENTER("QUICK_ROR_INTERSECT_SELECT::init");
 /* Check if last_rowid was successfully allocated in ctor */
  DBUG_RETURN(!last_rowid);
}


/*
  Initialize this quick select to be a ROR-merged scan.

  SYNOPSIS
    QUICK_RANGE_SELECT::init_ror_merged_scan()
      reuse_handler If TRUE, use head->file, otherwise create a separate
                    handler object

  NOTES
    This function creates and prepares for subsequent use a separate handler
    object if it can't reuse head->file. The reason for this is that during
    ROR-merge several key scans are performed simultaneously, and a single
    handler is only capable of preserving context of a single key scan.

    In ROR-merge the quick select doing merge does full records retrieval,
    merged quick selects read only keys.

  RETURN
    0  ROR child scan initialized, ok to use.
    1  error
*/

int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler,
                                             MEM_ROOT *local_alloc)
{
  handler *save_file= file, *org_file;
  THD *thd= head->in_use;
  MY_BITMAP * const save_read_set= head->read_set;
  MY_BITMAP * const save_write_set= head->write_set;
  DBUG_ENTER("QUICK_RANGE_SELECT::init_ror_merged_scan");

  in_ror_merged_scan= 1;
  if (reuse_handler)
  {
    DBUG_PRINT("info", ("Reusing handler %p", file));
    if (init())
    {
      DBUG_RETURN(1);
    }
    goto end;
  }

  /* Create a separate handler object for this quick select */
  if (free_file)
  {
    /* already have own 'handler' object. */
    DBUG_RETURN(0);
  }

  if (!(file= head->file->clone(head->s->normalized_path.str, local_alloc)))
  {
    /* clone() has already generated an error message */
    /* Caller will free the memory */
    goto failure;  /* purecov: inspected */
  }

  if (file->ha_external_lock(thd, F_RDLCK))
    goto failure;

  if (init())
  {
    file->ha_external_unlock(thd);
    file->ha_close();
    goto failure;
  }
  free_file= TRUE;
  last_rowid= file->ref;

end:
  /*
    We are only going to read key fields and call position() on 'file'
    The following sets head->read_set (== column_bitmap) to only use this
    key. The 'column_bitmap' is used in ::get_next()
  */
  org_file= head->file;
  head->file= file;

  head->column_bitmaps_set_no_signal(&column_bitmap, &column_bitmap);
  head->prepare_for_keyread(index, &column_bitmap);
  head->prepare_for_position();

  head->file= org_file;

  /* Restore head->read_set (and write_set) to what they had before the call */
  head->column_bitmaps_set(save_read_set, save_write_set);
 
  if (reset())
  {
    if (!reuse_handler)
    {
      file->ha_external_unlock(thd);
      file->ha_close();
      goto failure;
    }
    DBUG_RETURN(1);
  }
  DBUG_RETURN(0);

failure:
  head->column_bitmaps_set(save_read_set, save_write_set);
  delete file;
  file= save_file;
  free_file= false;
  DBUG_RETURN(1);
}


/*
  Initialize this quick select to be a part of a ROR-merged scan.
  SYNOPSIS
    QUICK_ROR_INTERSECT_SELECT::init_ror_merged_scan()
      reuse_handler If TRUE, use head->file, otherwise create separate
                    handler object.
  RETURN
    0     OK
    other error code
*/
int QUICK_ROR_INTERSECT_SELECT::init_ror_merged_scan(bool reuse_handler, 
                                                     MEM_ROOT *local_alloc)
{
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> quick_it(quick_selects);
  QUICK_SELECT_WITH_RECORD *cur;
  QUICK_RANGE_SELECT *quick;
  DBUG_ENTER("QUICK_ROR_INTERSECT_SELECT::init_ror_merged_scan");

  /* Initialize all merged "children" quick selects */
  DBUG_ASSERT(!need_to_fetch_row || reuse_handler);
  if (!need_to_fetch_row && reuse_handler)
  {
    cur= quick_it++;
    quick= cur->quick;
    /*
      There is no use of this->file. Use it for the first of merged range
      selects.
    */
    int error= quick->init_ror_merged_scan(TRUE, local_alloc);
    if (unlikely(error))
      DBUG_RETURN(error);
    quick->file->extra(HA_EXTRA_KEYREAD_PRESERVE_FIELDS);
  }
  while ((cur= quick_it++))
  {
    quick= cur->quick;
#ifndef DBUG_OFF
    const MY_BITMAP * const save_read_set= quick->head->read_set;
    const MY_BITMAP * const save_write_set= quick->head->write_set;
#endif
    if (quick->init_ror_merged_scan(FALSE, local_alloc))
      DBUG_RETURN(1);
    quick->file->extra(HA_EXTRA_KEYREAD_PRESERVE_FIELDS);

    // Sets are shared by all members of "quick_selects" so must not change
#ifndef DBUG_OFF
    DBUG_ASSERT(quick->head->read_set == save_read_set);
    DBUG_ASSERT(quick->head->write_set == save_write_set);
#endif
    /* All merged scans share the same record buffer in intersection. */
    quick->record= head->record[0];
  }

  if (need_to_fetch_row &&
      unlikely(head->file->ha_rnd_init_with_error(false)))
  {
    DBUG_PRINT("error", ("ROR index_merge rnd_init call failed"));
    DBUG_RETURN(1);
  }
  DBUG_RETURN(0);
}


/*
  Initialize quick select for row retrieval.
  SYNOPSIS
    reset()
  RETURN
    0      OK
    other  Error code
*/

int QUICK_ROR_INTERSECT_SELECT::reset()
{
  DBUG_ENTER("QUICK_ROR_INTERSECT_SELECT::reset");
  if (!scans_inited && init_ror_merged_scan(TRUE, &alloc))
    DBUG_RETURN(1);
  scans_inited= TRUE;
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);
  QUICK_SELECT_WITH_RECORD *qr;
  while ((qr= it++))
    qr->quick->reset();
  DBUG_RETURN(0);
}


/*
  Add a merged quick select to this ROR-intersection quick select.

  SYNOPSIS
    QUICK_ROR_INTERSECT_SELECT::push_quick_back()
      alloc Mem root to create auxiliary structures on
      quick Quick select to be added. The quick select must return
            rows in rowid order.
  NOTES
    This call can only be made before init() is called.

  RETURN
    FALSE OK
    TRUE  Out of memory.
*/

bool
QUICK_ROR_INTERSECT_SELECT::push_quick_back(MEM_ROOT *local_alloc,
                                            QUICK_RANGE_SELECT *quick)
{
  QUICK_SELECT_WITH_RECORD *qr;
  if (!(qr= new QUICK_SELECT_WITH_RECORD) || 
      !(qr->key_tuple= (uchar*)alloc_root(local_alloc,
                                          quick->max_used_key_length)))
    return TRUE;
  qr->quick= quick;
  return quick_selects.push_back(qr);
}


QUICK_ROR_INTERSECT_SELECT::~QUICK_ROR_INTERSECT_SELECT()
{
  DBUG_ENTER("QUICK_ROR_INTERSECT_SELECT::~QUICK_ROR_INTERSECT_SELECT");
  quick_selects.delete_elements();
  delete cpk_quick;
  free_root(&alloc,MYF(0));
  if (need_to_fetch_row && head->file->inited != handler::NONE)
    head->file->ha_rnd_end();
  DBUG_VOID_RETURN;
}


QUICK_ROR_UNION_SELECT::QUICK_ROR_UNION_SELECT(THD *thd_param,
                                               TABLE *table)
  : thd(thd_param), scans_inited(FALSE)
{
  index= MAX_KEY;
  head= table;
  rowid_length= table->file->ref_length;
  record= head->record[0];
  init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                 thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
  thd_param->mem_root= &alloc;
}


/*
  Comparison function to be used QUICK_ROR_UNION_SELECT::queue priority
  queue.

  SYNPOSIS
    QUICK_ROR_UNION_SELECT_queue_cmp()
      arg   Pointer to QUICK_ROR_UNION_SELECT
      val1  First merged select
      val2  Second merged select
*/

C_MODE_START

static int QUICK_ROR_UNION_SELECT_queue_cmp(void *arg, const void *val1_,
                                            const void *val2_)
{
  auto self= static_cast<QUICK_ROR_UNION_SELECT *>(arg);
  auto val1= static_cast<const QUICK_SELECT_I *>(val1_);
  auto val2= static_cast<const QUICK_SELECT_I *>(val2_);
  return self->head->file->cmp_ref(val1->last_rowid, val2->last_rowid);
}

C_MODE_END


/*
  Do post-constructor initialization.
  SYNOPSIS
    QUICK_ROR_UNION_SELECT::init()

  RETURN
    0      OK
    other  Error code
*/

int QUICK_ROR_UNION_SELECT::init()
{
  DBUG_ENTER("QUICK_ROR_UNION_SELECT::init");
  if (init_queue(&queue, quick_selects.elements, 0,
                 FALSE , QUICK_ROR_UNION_SELECT_queue_cmp,
                 (void*) this, 0, 0))
  {
    bzero(&queue, sizeof(QUEUE));
    DBUG_RETURN(1);
  }

  if (!(cur_rowid= (uchar*) alloc_root(&alloc, 2*head->file->ref_length)))
    DBUG_RETURN(1);
  prev_rowid= cur_rowid + head->file->ref_length;
  DBUG_RETURN(0);
}


/*
  Initialize quick select for row retrieval.
  SYNOPSIS
    reset()

  RETURN
    0      OK
    other  Error code
*/

int QUICK_ROR_UNION_SELECT::reset()
{
  QUICK_SELECT_I *quick;
  int error;
  DBUG_ENTER("QUICK_ROR_UNION_SELECT::reset");
  have_prev_rowid= FALSE;
  if (!scans_inited)
  {
    List_iterator_fast<QUICK_SELECT_I> it(quick_selects);
    while ((quick= it++))
    {
      if (quick->init_ror_merged_scan(FALSE, &alloc))
        DBUG_RETURN(1);
    }
    scans_inited= TRUE;
  }
  queue_remove_all(&queue);
  /*
    Initialize scans for merged quick selects and put all merged quick
    selects into the queue.
  */
  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);
  while ((quick= it++))
  {
    if (unlikely((error= quick->reset())))
      DBUG_RETURN(error);
    if (unlikely((error= quick->get_next())))
    {
      if (error == HA_ERR_END_OF_FILE)
        continue;
      DBUG_RETURN(error);
    }
    quick->save_last_pos();
    queue_insert(&queue, (uchar*)quick);
  }
  /* Prepare for ha_rnd_pos calls. */
  if (head->file->inited && unlikely((error= head->file->ha_rnd_end())))
  {
    DBUG_PRINT("error", ("ROR index_merge rnd_end call failed"));
    DBUG_RETURN(error);
  }
  if (unlikely((error= head->file->ha_rnd_init(false))))
  {
    DBUG_PRINT("error", ("ROR index_merge rnd_init call failed"));
    DBUG_RETURN(error);
  }

  DBUG_RETURN(0);
}


bool
QUICK_ROR_UNION_SELECT::push_quick_back(QUICK_SELECT_I *quick_sel_range)
{
  return quick_selects.push_back(quick_sel_range);
}

QUICK_ROR_UNION_SELECT::~QUICK_ROR_UNION_SELECT()
{
  DBUG_ENTER("QUICK_ROR_UNION_SELECT::~QUICK_ROR_UNION_SELECT");
  delete_queue(&queue);
  quick_selects.delete_elements();
  if (head->file->inited != handler::NONE)
    head->file->ha_rnd_end();
  free_root(&alloc,MYF(0));
  DBUG_VOID_RETURN;
}


QUICK_RANGE::QUICK_RANGE()
  :min_key(0),max_key(0),min_length(0),max_length(0),
   flag(NO_MIN_RANGE | NO_MAX_RANGE),
  min_keypart_map(0), max_keypart_map(0)
{}

SEL_ARG::SEL_ARG(SEL_ARG &arg) :Sql_alloc()
{
  type=arg.type;
  min_flag=arg.min_flag;
  max_flag=arg.max_flag;
  maybe_flag=arg.maybe_flag;
  maybe_null=arg.maybe_null;
  part=arg.part;
  field=arg.field;
  min_value=arg.min_value;
  max_value=arg.max_value;
  next_key_part=arg.next_key_part;
  max_part_no= arg.max_part_no;
  use_count=1; elements=1;
  weight=1;
  next= 0;
  if (next_key_part)
  {
    next_key_part->increment_use_count(1);
    weight += next_key_part->weight;
  }
}


inline void SEL_ARG::make_root()
{
  left=right= &null_element;
  color=BLACK;
  next=prev=0;
  use_count=0;
  elements=1;
  weight= 1 + (next_key_part? next_key_part->weight : 0);
}

SEL_ARG::SEL_ARG(Field *f, const uchar *min_value_arg,
                 const uchar *max_value_arg)
  :min_flag(0), max_flag(0), maybe_flag(0), maybe_null(f->real_maybe_null()),
   elements(1), use_count(1), field(f), min_value((uchar*) min_value_arg),
   max_value((uchar*) max_value_arg), next(0),prev(0),
   next_key_part(0), color(BLACK), type(KEY_RANGE), weight(1)
{
  left=right= &null_element;
  max_part_no= 1;
}

SEL_ARG::SEL_ARG(Field *field_,uint8 part_,
                 uchar *min_value_, uchar *max_value_,
		 uint8 min_flag_,uint8 max_flag_,uint8 maybe_flag_)
  :min_flag(min_flag_),max_flag(max_flag_),maybe_flag(maybe_flag_),
   part(part_),maybe_null(field_->real_maybe_null()),
   elements(1),use_count(1),
   field(field_), min_value(min_value_), max_value(max_value_),
   next(0),prev(0),next_key_part(0),color(BLACK),type(KEY_RANGE), weight(1)
{
  max_part_no= part+1;
  left=right= &null_element;
}


/*
  A number of helper classes:
    SEL_ARG_LE, SEL_ARG_LT, SEL_ARG_GT, SEL_ARG_GE,
  to share the code between:
    Field::stored_field_make_mm_leaf()
    Field::stored_field_make_mm_leaf_exact()
*/
class SEL_ARG_LE: public SEL_ARG
{
public:
  SEL_ARG_LE(const uchar *key, Field *field)
   :SEL_ARG(field, key, key)
  {
    if (!field->real_maybe_null())
      min_flag= NO_MIN_RANGE;     // From start
    else
    {
      min_value= is_null_string;
      min_flag= NEAR_MIN;        // > NULL
    }
  }
};


class SEL_ARG_LT: public SEL_ARG_LE
{
public:
  /*
    Use this constructor if value->save_in_field() went precisely,
    without any data rounding or truncation.
  */
  SEL_ARG_LT(const uchar *key, const KEY_PART *key_part, Field *field)
   :SEL_ARG_LE(key, field)
  {
    // Don't use open ranges for partial key_segments
    if (!(key_part->flag & HA_PART_KEY_SEG))
      max_flag= NEAR_MAX;
  }
  /*
    Use this constructor if value->save_in_field() returned success,
    but we don't know if rounding or truncation happened
    (as some Field::store() do not report minor data changes).
  */
  SEL_ARG_LT(THD *thd, const uchar *key,
             const KEY_PART *key_part, Field *field, Item *value)
   :SEL_ARG_LE(key, field)
  {
    // Don't use open ranges for partial key_segments
    if (!(key_part->flag & HA_PART_KEY_SEG) &&
        stored_field_cmp_to_item(thd, field, value) == 0)
      max_flag= NEAR_MAX;
  }
};


class SEL_ARG_GT: public SEL_ARG
{
public:
  /*
    Use this constructor if value->save_in_field() went precisely,
    without any data rounding or truncation.
  */
  SEL_ARG_GT(const uchar *key, const KEY_PART *key_part, Field *field)
   :SEL_ARG(field, key, key)
  {
    // Don't use open ranges for partial key_segments
    if (!(key_part->flag & HA_PART_KEY_SEG))
      min_flag= NEAR_MIN;
    max_flag= NO_MAX_RANGE;
  }
  /*
    Use this constructor if value->save_in_field() returned success,
    but we don't know if rounding or truncation happened
    (as some Field::store() do not report minor data changes).
  */
  SEL_ARG_GT(THD *thd, const uchar *key,
             const KEY_PART *key_part, Field *field, Item *value)
   :SEL_ARG(field, key, key)
  {
    // Don't use open ranges for partial key_segments
    if ((!(key_part->flag & HA_PART_KEY_SEG)) &&
        (stored_field_cmp_to_item(thd, field, value) <= 0))
      min_flag= NEAR_MIN;
    max_flag= NO_MAX_RANGE;
  }
};


class SEL_ARG_GE: public SEL_ARG
{
public:
  /*
    Use this constructor if value->save_in_field() went precisely,
    without any data rounding or truncation.
  */
  SEL_ARG_GE(const uchar *key, Field *field)
   :SEL_ARG(field, key, key)
  {
    max_flag= NO_MAX_RANGE;
  }
  /*
    Use this constructor if value->save_in_field() returned success,
    but we don't know if rounding or truncation happened
    (as some Field::store() do not report minor data changes).
  */
  SEL_ARG_GE(THD *thd, const uchar *key,
             const KEY_PART *key_part, Field *field, Item *value)
   :SEL_ARG(field, key, key)
  {
    // Don't use open ranges for partial key_segments
    if ((!(key_part->flag & HA_PART_KEY_SEG)) &&
        (stored_field_cmp_to_item(thd, field, value) < 0))
      min_flag= NEAR_MIN;
    max_flag= NO_MAX_RANGE;
  }
};


SEL_ARG *SEL_ARG::clone(RANGE_OPT_PARAM *param, SEL_ARG *new_parent, 
                        SEL_ARG **next_arg)
{
  SEL_ARG *tmp;

  /* Bail out if we have already generated too many SEL_ARGs */
  if (++param->alloced_sel_args > param->thd->variables.optimizer_max_sel_args)
    return 0;

  if (type != KEY_RANGE)
  {
    if (!(tmp= new (param->mem_root) SEL_ARG(type)))
      return 0;					// out of memory
    tmp->prev= *next_arg;			// Link into next/prev chain
    (*next_arg)->next=tmp;
    (*next_arg)= tmp;
    tmp->part= this->part;
  }
  else
  {
    if (!(tmp= new (param->mem_root) SEL_ARG(field, part,
                                             min_value, max_value,
                                             min_flag, max_flag, maybe_flag)))
      return 0;					// OOM
    tmp->parent=new_parent;
    tmp->next_key_part=next_key_part;
    if (left != &null_element)
      if (!(tmp->left=left->clone(param, tmp, next_arg)))
	return 0;				// OOM

    tmp->prev= *next_arg;			// Link into next/prev chain
    (*next_arg)->next=tmp;
    (*next_arg)= tmp;

    if (right != &null_element)
      if (!(tmp->right= right->clone(param, tmp, next_arg)))
	return 0;				// OOM
  }
  increment_use_count(1);
  tmp->color= color;
  tmp->elements= this->elements;
  tmp->max_part_no= max_part_no;
  tmp->weight= weight;
  return tmp;
}

/**
  This gives the first SEL_ARG in the interval list, and the minimal element
  in the red-black tree

  @return
  SEL_ARG   first SEL_ARG in the interval list
*/
SEL_ARG *SEL_ARG::first()
{
  SEL_ARG *next_arg=this;
  if (!next_arg->left)
    return 0;					// MAYBE_KEY
  while (next_arg->left != &null_element)
    next_arg=next_arg->left;
  return next_arg;
}

const SEL_ARG *SEL_ARG::first() const
{
  return const_cast<SEL_ARG*>(this)->first();
}

SEL_ARG *SEL_ARG::last()
{
  SEL_ARG *next_arg=this;
  if (!next_arg->right)
    return 0;					// MAYBE_KEY
  while (next_arg->right != &null_element)
    next_arg=next_arg->right;
  return next_arg;
}


/*
  Check if a compare is ok, when one takes ranges in account
  Returns -2 or 2 if the ranges where 'joined' like  < 2 and >= 2
*/

int SEL_ARG::sel_cmp(Field *field, uchar *a, uchar *b, uint8 a_flag,
                     uint8 b_flag)
{
  int cmp;
  /* First check if there was a compare to a min or max element */
  if (a_flag & (NO_MIN_RANGE | NO_MAX_RANGE))
  {
    if ((a_flag & (NO_MIN_RANGE | NO_MAX_RANGE)) ==
	(b_flag & (NO_MIN_RANGE | NO_MAX_RANGE)))
      return 0;
    return (a_flag & NO_MIN_RANGE) ? -1 : 1;
  }
  if (b_flag & (NO_MIN_RANGE | NO_MAX_RANGE))
    return (b_flag & NO_MIN_RANGE) ? 1 : -1;

  if (field->real_maybe_null())			// If null is part of key
  {
    if (*a != *b)
    {
      return *a ? -1 : 1;
    }
    if (*a)
      goto end;					// NULL where equal
    a++; b++;					// Skip NULL marker
  }
  cmp=field->key_cmp(a , b);
  if (cmp) return cmp < 0 ? -1 : 1;		// The values differed

  // Check if the compared equal arguments was defined with open/closed range
 end:
  if (a_flag & (NEAR_MIN | NEAR_MAX))
  {
    if ((a_flag & (NEAR_MIN | NEAR_MAX)) == (b_flag & (NEAR_MIN | NEAR_MAX)))
      return 0;
    if (!(b_flag & (NEAR_MIN | NEAR_MAX)))
      return (a_flag & NEAR_MIN) ? 2 : -2;
    return (a_flag & NEAR_MIN) ? 1 : -1;
  }
  if (b_flag & (NEAR_MIN | NEAR_MAX))
    return (b_flag & NEAR_MIN) ? -2 : 2;
  return 0;					// The elements where equal
}


/*
  Check if min and values are equal

  @return 1 if equal
*/

bool SEL_ARG::min_max_are_equal() const
{
  uint offset= 0;
  if (field->real_maybe_null())			// If null is part of key
  {
    if (*min_value != *max_value)
      return 0;
    if (*min_value)
      return 1;					// NULL where equal
    offset= 1;                                  // Skip NULL marker
  }
  return field->key_cmp(min_value+offset, max_value+offset) == 0;
}


SEL_ARG *SEL_ARG::clone_tree(RANGE_OPT_PARAM *param)
{
  SEL_ARG tmp_link,*next_arg,*root;
  next_arg= &tmp_link;
  if (!(root= clone(param, (SEL_ARG *) 0, &next_arg)))
    return 0;
  next_arg->next=0;				// Fix last link
  tmp_link.next->prev=0;			// Fix first link
  if (root)					// If not OOM
    root->use_count= 0;
  return root;
}


/*
  Table rows retrieval plan. Range optimizer creates QUICK_SELECT_I-derived
  objects from table read plans.
*/
class TABLE_READ_PLAN
{
public:
  /*
    An INDEX_MERGE hint was present in the query that created this
    read plan, so preserve that fact for the QUICK_SELECT that will
    be created as a result.  The QUICK_SELECT will use it to override
    plan selection to ensure that index merge is used when possible
    (it will not be possible if the read plan is a range read plan and
    there are less-than two available ROR scans).
  */
  bool force_index_merge{false};

  /*
    Plan read cost, with or without cost of full row retrieval, depending
    on plan creation parameters.
  */
  double read_cost;
  ha_rows records; /* estimate of #rows to be examined */

  /*
    If TRUE, the scan returns rows in rowid order. This is used only for
    scans that can be both ROR and non-ROR.
  */
  bool is_ror;

  /*
    Create quick select for this plan.
    SYNOPSIS
     make_quick()
       param               Parameter from test_quick_select
       retrieve_full_rows  If TRUE, created quick select will do full record
                           retrieval.
       parent_alloc        Memory pool to use, if any.

    NOTES
      retrieve_full_rows is ignored by some implementations.

    RETURN
      created quick select
      NULL on any error.
  */
  virtual QUICK_SELECT_I *make_quick(PARAM *param,
                                     bool retrieve_full_rows,
                                     MEM_ROOT *parent_alloc=NULL) = 0;

  /* Table read plans are allocated on MEM_ROOT and are never deleted */
  static void *operator new(size_t size, MEM_ROOT *mem_root)
  { return (void*) alloc_root(mem_root, (uint) size); }
  static void operator delete(void *ptr,size_t size) { TRASH_FREE(ptr, size); }
  static void operator delete(void *ptr, MEM_ROOT *mem_root) { /* Never called */ }
  virtual ~TABLE_READ_PLAN() = default;               /* Remove gcc warning */
  /**
     Add basic info for this TABLE_READ_PLAN to the optimizer trace.

     @param param        Parameters for range analysis of this table
     @param trace_object The optimizer trace object the info is appended to
  */
  virtual void trace_basic_info(PARAM *param,
                                Json_writer_object *trace_object) const= 0;

};

class TRP_ROR_INTERSECT;
class TRP_ROR_UNION;
class TRP_INDEX_MERGE;


/*
  Plan for a QUICK_RANGE_SELECT scan.
  TRP_RANGE::make_quick ignores retrieve_full_rows parameter because
  QUICK_RANGE_SELECT doesn't distinguish between 'index only' scans and full
  record retrieval scans.
*/

class TRP_RANGE : public TABLE_READ_PLAN
{
public:
  SEL_ARG *key; /* set of intervals to be used in "range" method retrieval */
  uint     key_idx; /* key number in PARAM::key */
  uint     mrr_flags; 
  uint     mrr_buf_size;

  TRP_RANGE(SEL_ARG *key_arg, uint idx_arg, uint mrr_flags_arg)
   : key(key_arg), key_idx(idx_arg), mrr_flags(mrr_flags_arg)
  {}
  ~TRP_RANGE() override = default;                     /* Remove gcc warning */

  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override
  {
    DBUG_ENTER("TRP_RANGE::make_quick");
    QUICK_RANGE_SELECT *quick;
    if ((quick= get_quick_select(param, key_idx, key,  mrr_flags, 
                                 mrr_buf_size, parent_alloc)))
    {
      quick->records= records;
      quick->read_time= read_cost;
    }
    DBUG_RETURN(quick);
  }
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;
};

void TRP_RANGE::trace_basic_info(PARAM *param,
                                 Json_writer_object *trace_object) const
{
  DBUG_ASSERT(trace_object->trace_started());
  DBUG_ASSERT(param->using_real_indexes);
  const uint keynr_in_table= param->real_keynr[key_idx];

  const KEY &cur_key= param->table->key_info[keynr_in_table];
  const KEY_PART_INFO *key_part= cur_key.key_part;

  if (unlikely(trace_object->trace_started()))
    trace_object->
      add("type", "range_scan").
      add("index", cur_key.name).
      add("rows", records);

  Json_writer_array trace_range(param->thd, "ranges");

  // TRP_RANGE should not be created if there are no range intervals
  DBUG_ASSERT(key);

  trace_ranges(&trace_range, param, key_idx, key, key_part);
}


/* Plan for QUICK_ROR_INTERSECT_SELECT scan. */

class TRP_ROR_INTERSECT : public TABLE_READ_PLAN
{
public:
  TRP_ROR_INTERSECT() = default;                      /* Remove gcc warning */
  ~TRP_ROR_INTERSECT() override = default;             /* Remove gcc warning */
  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override;

  /* Array of pointers to ROR range scans used in this intersection */
  struct st_ror_scan_info **first_scan;
  struct st_ror_scan_info **last_scan; /* End of the above array */
  struct st_ror_scan_info *cpk_scan;  /* Clustered PK scan, if there is one */
  bool is_covering; /* TRUE if no row retrieval phase is necessary */
  double index_scan_costs; /* SUM(cost(index_scan)) */
  double cmp_cost;         // Cost of out rows with WHERE clause
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;
};



/*
  Plan for QUICK_ROR_UNION_SELECT scan.
  QUICK_ROR_UNION_SELECT always retrieves full rows, so retrieve_full_rows
  is ignored by make_quick.
*/

class TRP_ROR_UNION : public TABLE_READ_PLAN
{
public:
  TRP_ROR_UNION() = default;                          /* Remove gcc warning */
  ~TRP_ROR_UNION() override = default;                 /* Remove gcc warning */
  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override;
  TABLE_READ_PLAN **first_ror; /* array of ptrs to plans for merged scans */
  TABLE_READ_PLAN **last_ror;  /* end of the above array */
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;
};

void TRP_ROR_UNION::trace_basic_info(PARAM *param,
                                     Json_writer_object *trace_object) const
{
  THD *thd= param->thd;
  DBUG_ASSERT(trace_object->trace_started());
  trace_object->add("type", "index_roworder_union");
  Json_writer_array smth_trace(thd, "union_of");
  for (TABLE_READ_PLAN **current= first_ror; current != last_ror; current++)
  {
    Json_writer_object trp_info(thd);
    (*current)->trace_basic_info(param, &trp_info);
  }
}

/*
  Plan for QUICK_INDEX_INTERSECT_SELECT scan.
  QUICK_INDEX_INTERSECT_SELECT always retrieves full rows, so retrieve_full_rows
  is ignored by make_quick.
*/

class TRP_INDEX_INTERSECT : public TABLE_READ_PLAN
{
public:
  TRP_INDEX_INTERSECT() = default;                     /* Remove gcc warning */
  ~TRP_INDEX_INTERSECT() override = default;            /* Remove gcc warning */
  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override;
  TRP_RANGE **range_scans; /* array of ptrs to plans of intersected scans */
  TRP_RANGE **range_scans_end; /* end of the array */
  /* keys whose scans are to be filtered by cpk conditions */
  key_map filtered_scans;
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;

};

void TRP_INDEX_INTERSECT::trace_basic_info(PARAM *param,
                                       Json_writer_object *trace_object) const
{
  THD *thd= param->thd;
  DBUG_ASSERT(trace_object->trace_started());
  trace_object->add("type", "index_sort_intersect");
  Json_writer_array smth_trace(thd, "index_sort_intersect_of");
  for (TRP_RANGE **current= range_scans; current != range_scans_end;
                                                          current++)
  {
    Json_writer_object trp_info(thd);
    (*current)->trace_basic_info(param, &trp_info);
  }
}

/*
  Plan for QUICK_INDEX_MERGE_SELECT scan.
  QUICK_ROR_INTERSECT_SELECT always retrieves full rows, so retrieve_full_rows
  is ignored by make_quick.
*/

class TRP_INDEX_MERGE : public TABLE_READ_PLAN
{
public:
  TRP_INDEX_MERGE() = default;                        /* Remove gcc warning */
  ~TRP_INDEX_MERGE() override = default;               /* Remove gcc warning */
  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override;
  TRP_RANGE **range_scans; /* array of ptrs to plans of merged scans */
  TRP_RANGE **range_scans_end; /* end of the array */
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;
};

void TRP_INDEX_MERGE::trace_basic_info(PARAM *param,
                                       Json_writer_object *trace_object) const
{
  THD *thd= param->thd;
  DBUG_ASSERT(trace_object->trace_started());
  trace_object->add("type", "index_merge");
  Json_writer_array smth_trace(thd, "index_merge_of");
  for (TRP_RANGE **current= range_scans; current != range_scans_end; current++)
  {
    Json_writer_object trp_info(thd);
    (*current)->trace_basic_info(param, &trp_info);
  }
}

/*
  Plan for a QUICK_GROUP_MIN_MAX_SELECT scan. 
*/

class TRP_GROUP_MIN_MAX : public TABLE_READ_PLAN
{
private:
  uint group_prefix_len;
  uint used_key_parts;
  uint group_key_parts;
  uint index;
  uint key_infix_len;
  uint param_idx; /* Index of used key in param->key. */
  uchar key_infix[MAX_KEY_LENGTH];
  KEY *index_info;
  KEY_PART_INFO *min_max_arg_part;
  SEL_TREE *range_tree; /* Represents all range predicates in the query. */
  SEL_ARG  *index_tree; /* The SEL_ARG sub-tree corresponding to index_info. */
  bool have_min, have_max;
public:
  bool have_agg_distinct;
  bool is_index_scan; /* Use index_next() instead of random read */
  /* Number of records selected by the ranges in index_tree. */
  ha_rows quick_prefix_records;
public:
  TRP_GROUP_MIN_MAX(bool have_min_arg, bool have_max_arg, 
                    bool have_agg_distinct_arg,
                    KEY_PART_INFO *min_max_arg_part_arg,
                    uint group_prefix_len_arg, uint used_key_parts_arg,
                    uint group_key_parts_arg, KEY *index_info_arg,
                    uint index_arg, uint key_infix_len_arg,
                    uchar *key_infix_arg,
                    SEL_TREE *tree_arg, SEL_ARG *index_tree_arg,
                    uint param_idx_arg, ha_rows quick_prefix_records_arg)
  : group_prefix_len(group_prefix_len_arg), used_key_parts(used_key_parts_arg),
    group_key_parts(group_key_parts_arg),
    index(index_arg), key_infix_len(key_infix_len_arg), param_idx(param_idx_arg),
    index_info(index_info_arg),min_max_arg_part(min_max_arg_part_arg),
    range_tree(tree_arg), index_tree(index_tree_arg),
    have_min(have_min_arg), have_max(have_max_arg),
    have_agg_distinct(have_agg_distinct_arg),
    is_index_scan(FALSE),
    quick_prefix_records(quick_prefix_records_arg)
    {
      if (key_infix_len)
        memcpy(this->key_infix, key_infix_arg, key_infix_len);
    }
  ~TRP_GROUP_MIN_MAX() override = default;             /* Remove gcc warning */

  QUICK_SELECT_I *make_quick(PARAM *param, bool retrieve_full_rows,
                             MEM_ROOT *parent_alloc) override;
  void use_index_scan() { is_index_scan= TRUE; }
  void trace_basic_info(PARAM *param,
                        Json_writer_object *trace_object) const override;
};


void TRP_GROUP_MIN_MAX::trace_basic_info(PARAM *param,
                                Json_writer_object *trace_object) const
{
  THD *thd= param->thd;
  DBUG_ASSERT(trace_object->trace_started());

  trace_object->add("type", "index_group").add("index", index_info->name);

  if (min_max_arg_part)
    trace_object->add("min_max_arg", min_max_arg_part->field->field_name);
  else
    trace_object->add_null("min_max_arg");

  if (unlikely(trace_object->trace_started()))
    trace_object->
      add("min_aggregate", have_min).
      add("max_aggregate", have_max).
      add("distinct_aggregate", have_agg_distinct).
      add("rows", records).
      add("cost", read_cost);

  const KEY_PART_INFO *key_part= index_info->key_part;
  {
    Json_writer_array trace_keyparts(thd, "key_parts_used_for_access");
    for (uint partno= 0; partno < used_key_parts; partno++)
    {
      const KEY_PART_INFO *cur_key_part= key_part + partno;
      trace_keyparts.add(cur_key_part->field->field_name);
    }
  }

  Json_writer_array trace_range(thd, "ranges");

  // can have group quick without ranges
  if (index_tree)
  {
    trace_ranges(&trace_range, param, param_idx,
                 index_tree, key_part);
  }
}


typedef struct st_index_scan_info
{
  uint      idx;      /* # of used key in param->keys */
  uint      keynr;    /* # of used key in table */
  uint      range_count;
  ha_rows   records;  /* estimate of # records this scan will return */

  /* Set of intervals over key fields that will be used for row retrieval. */
  SEL_ARG   *sel_arg;

  KEY *key_info;
  uint used_key_parts;

  /* Estimate of # records filtered out by intersection with cpk */
  ha_rows   filtered_out;
  /* Bitmap of fields used in index intersection */ 
  MY_BITMAP used_fields;

  /* Fields used in the query and covered by ROR scan. */
  MY_BITMAP covered_fields;
  uint      used_fields_covered; /* # of set bits in covered_fields */
  int       key_rec_length; /* length of key record (including rowid) */

  /*
    Cost of reading all index records with values in sel_arg intervals set
    (assuming there is no need to access full table records)
  */
  double    index_read_cost;
  uint      first_uncovered_field; /* first unused bit in covered_fields */
  uint      key_components; /* # of parts in the key */
} INDEX_SCAN_INFO;

/*
  Fill param->needed_fields with bitmap of fields used in the query.
  SYNOPSIS
    fill_used_fields_bitmap()
      param Parameter from test_quick_select function.

  NOTES
    Clustered PK members are not put into the bitmap as they are implicitly
    present in all keys (and it is impossible to avoid reading them).
  RETURN
    0  Ok
    1  Out of memory.
*/

static int fill_used_fields_bitmap(PARAM *param)
{
  TABLE *table= param->table;
  my_bitmap_map *tmp;
  uint pk;
  param->tmp_covered_fields.bitmap= 0;
  param->fields_bitmap_size= table->s->column_bitmap_size;
  if (!(tmp= (my_bitmap_map*) alloc_root(param->mem_root,
                                  param->fields_bitmap_size)) ||
      my_bitmap_init(&param->needed_fields, tmp, table->s->fields))
    return 1;

  bitmap_copy(&param->needed_fields, table->read_set);
  bitmap_union(&param->needed_fields, table->write_set);

  pk= param->table->s->primary_key;
  if (param->table->file->pk_is_clustering_key(pk))
  {
    /* The table uses clustered PK and it is not internally generated */
    KEY_PART_INFO *key_part= param->table->key_info[pk].key_part;
    KEY_PART_INFO *key_part_end= key_part +
                                 param->table->key_info[pk].user_defined_key_parts;
    for (;key_part != key_part_end; ++key_part)
      bitmap_clear_bit(&param->needed_fields, key_part->fieldnr-1);
  }
  return 0;
}


/*
  Test if a key can be used in different ranges

  SYNOPSIS
    SQL_SELECT::test_quick_select()
      thd               Current thread
      keys_to_use       Keys to use for range retrieval
      prev_tables       Tables assumed to be already read when the scan is
                        performed (but not read at the moment of this call)
      limit             Query limit
      force_quick_range Prefer to use range (instead of full table scan) even
                        if it is more expensive.
      remove_false_parts_of_where  Remove parts of OR-clauses for which range
                                   analysis produced SEL_TREE(IMPOSSIBLE)
      only_single_index_range_scan Evaluate only single index range scans

  NOTES
    Updates the following in the select parameter:
      needed_reg - Bits for keys with may be used if all prev regs are read
      quick      - Parameter to use when reading records.

    In the table struct the following information is updated:
      quick_keys           - Which keys can be used
      opt_range_condition_rows - E(# rows that will satisfy the table condition)

  IMPLEMENTATION
    opt_range_condition_rows value is obtained as follows:

      It is a minimum of E(#output rows) for all considered table access
      methods (range and index_merge accesses over various indexes).

    The obtained value is not a true E(#rows that satisfy table condition)
    but rather a pessimistic estimate. To obtain a true E(#...) one would
    need to combine estimates of various access methods, taking into account
    correlations between sets of rows they will return.

    For example, if values of tbl.key1 and tbl.key2 are independent (a right
    assumption if we have no information about their correlation) then the
    correct estimate will be:

      E(#rows("tbl.key1 < c1 AND tbl.key2 < c2")) =
      = E(#rows(tbl.key1 < c1)) / total_rows(tbl) * E(#rows(tbl.key2 < c2)

    which is smaller than

       MIN(E(#rows(tbl.key1 < c1), E(#rows(tbl.key2 < c2)))

    which is currently produced.

  TODO
   * Change the value returned in opt_range_condition_rows from a pessimistic
     estimate to true E(#rows that satisfy table condition).
     (we can re-use some of E(#rows) calculation code from
     index_merge/intersection for this)

   * Check if this function really needs to modify keys_to_use, and change the
     code to pass it by reference if it doesn't.

   * In addition to force_quick_range other means can be (an usually are) used
     to make this function prefer range over full table scan. Figure out if
     force_quick_range is really needed.

  RETURN
    SQL_SELECT::
      IMPOSSIBLE_RANGE,
        impossible select (i.e. certainly no rows will be selected)
      ERROR,
        an error occurred, either memory or in evaluating conditions
      OK = 1,
        either
          found usable ranges and quick select has been successfully created.
          or can't use quick_select
*/

quick_select_return
SQL_SELECT::test_quick_select(THD *thd,
                              key_map keys_to_use,
                              table_map prev_tables,
                              ha_rows limit, bool force_quick_range,
                              bool ordered_output,
                              bool remove_false_parts_of_where,
                              bool only_single_index_range_scan,
                              Item_func::Bitmap note_unusable_keys)
{
  DBUG_ENTER("SQL_SELECT::test_quick_select");
  DBUG_PRINT("enter",("keys_to_use: %lu  prev_tables: %lu  const_tables: %lu",
		      (ulong) keys_to_use.to_ulonglong(), (ulong) prev_tables,
		      (ulong) const_tables));

  ha_rows table_records= head->stat_records();
  DBUG_PRINT("info", ("records: %llu", (ulonglong) table_records));
  DBUG_ASSERT(table_records || !head->file->stats.records);

  delete quick;
  quick= nullptr;
  needed_reg.clear_all();
  quick_keys.clear_all();
  head->with_impossible_ranges.clear_all();
  DBUG_ASSERT(!head->is_filled_at_execution());
  quick_select_return returnval= OK;
  if (keys_to_use.is_clear_all() || head->is_filled_at_execution())
    DBUG_RETURN(returnval);
  records= table_records;
  handler *file= head->file;
  if (file->ha_table_flags() & HA_NON_COMPARABLE_ROWID)
    only_single_index_range_scan= 1;

  Item *notnull_cond= head->notnull_cond;
  if (head->force_index || force_quick_range)
  {
    DEBUG_SYNC(thd, "in_forced_range_optimize");
    read_time= DBL_MAX;
  }
  else
  {
    read_time= file->cost(file->ha_scan_and_compare_time(records));
    if (limit < records)
      notnull_cond= nullptr;
  }

  possible_keys.clear_all();

  DBUG_PRINT("info",("Time to scan table: %g", read_time));

  Json_writer_object table_info(thd);
  table_info.add_table_name(head);

  Json_writer_object trace_range(thd, "range_analysis");
  if (unlikely(thd->trace_started()) && read_time != DBL_MAX)
  {
    Json_writer_object table_rec(thd, "table_scan");
    table_rec.add("rows", records).add("cost", read_time);
  }

  keys_to_use.intersect(head->keys_in_use_for_query);
  if (keys_to_use.is_clear_all())
  {
    /*
      There are no keys available to use, so return now.  Assume that if the
      user is using 'limit' we will only need to scan limit rows if we are using
      a key.
    */
    set_if_smaller(records, table_records);
    DBUG_RETURN(returnval);
  }

  uchar buff[STACK_BUFF_ALLOC];
  MEM_ROOT alloc;
  SEL_TREE *tree= nullptr;
  SEL_TREE *notnull_cond_tree= nullptr;
  KEY_PART *key_parts;
  KEY *key_info;
  PARAM param;
  bool force_group_by= false, group_by_optimization_used= false;

  if (check_stack_overrun(thd, 2*STACK_MIN_SIZE + sizeof(PARAM), buff))
    DBUG_RETURN(ERROR);               // Fatal error flag is set

  /* set up parameter that is passed to all functions */
  bzero((void*) &param, sizeof(param));
  param.thd= thd;
  param.baseflag= file->ha_table_flags();
  param.prev_tables=prev_tables | const_tables;
  param.read_tables=read_tables;
  param.current_table= head->map;
  param.table=head;
  param.keys=0;
  param.mem_root= &alloc;
  param.old_root= thd->mem_root;
  param.needed_reg= &needed_reg;
  param.imerge_cost_buff_size= 0;
  param.using_real_indexes= TRUE;
  param.remove_jump_scans= TRUE;
  param.max_key_parts= 0;
  param.remove_false_where_parts= remove_false_parts_of_where;
  param.force_default_mrr= ordered_output;
  param.note_unusable_keys= thd->give_notes_for_unusable_keys() ?
                            note_unusable_keys :
                            Item_func::BITMAP_NONE;
  param.possible_keys.clear_all();

  thd->no_errors=1;				// Don't warn about nullptr
  init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                 thd->variables.range_alloc_block_size, 0,
                 MYF(MY_THREAD_SPECIFIC));
  if (!(param.key_parts=
         (KEY_PART*) alloc_root(&alloc,
                                sizeof(KEY_PART) *
                                head->s->actual_n_key_parts(thd))) ||
      fill_used_fields_bitmap(&param))
  {
    thd->no_errors=0;
    free_root(&alloc,MYF(0));			// Return memory & allocator
    DBUG_RETURN(ERROR);
  }
  key_parts= param.key_parts;

  /*
    Make an array with description of all key parts of all table keys.
    This is used in get_mm_parts function.
  */
  key_info= head->key_info;
  uint max_key_len= 0;

  Json_writer_array trace_idx(thd, "potential_range_indexes");

  for (uint idx=0 ; idx < head->s->keys ; idx++, key_info++)
  {
    Json_writer_object trace_idx_details(thd);
    trace_idx_details.add("index", key_info->name);
    KEY_PART_INFO *key_part_info;
    uint n_key_parts= head->actual_n_key_parts(key_info);

    if (!keys_to_use.is_set(idx))
    {
      if (unlikely(trace_idx_details.trace_started()))
        trace_idx_details.
          add("usable", false).
          add("cause", "not applicable");
      continue;
    }
    if (hint_key_state(thd, head, idx, NO_RANGE_HINT_ENUM, 0))
    {
      trace_idx_details.
          add("usable", false).
          add("cause", "no_range_optimization hint");
      continue;
    }
    if (key_info->algorithm == HA_KEY_ALG_FULLTEXT)
    {
      trace_idx_details.add("usable", false).add("cause", "fulltext");
      continue;    // ToDo: ft-keys in non-ft ranges, if possible   SerG
    }
    trace_idx_details.add("usable", true);
    param.key[param.keys]=key_parts;
    key_part_info= key_info->key_part;
    uint cur_key_len= 0;
    Json_writer_array trace_keypart(thd, "key_parts");
    for (uint part= 0 ; part < n_key_parts ;
         part++, key_parts++, key_part_info++)
    {
      key_parts->key= param.keys;
      key_parts->part= part;
      key_parts->length= key_part_info->length;
      key_parts->store_length= key_part_info->store_length;
      cur_key_len += key_part_info->store_length;
      key_parts->field=	key_part_info->field;
      key_parts->null_bit= key_part_info->null_bit;
      key_parts->image_type= Field::image_type(key_info->algorithm);
      /* Only HA_PART_KEY_SEG is used */
      key_parts->flag= (uint8) key_part_info->key_part_flag;
      trace_keypart.add(key_parts->field->field_name);
    }
    trace_keypart.end();
    param.real_keynr[param.keys++]=idx;
    if (cur_key_len > max_key_len)
      max_key_len= cur_key_len;
  }
  trace_idx.end();

  param.key_parts_end=key_parts;
  param.alloced_sel_args= 0;

  max_key_len++; /* Take into account the "+1" in QUICK_RANGE::QUICK_RANGE */
  if (!(param.min_key= (uchar*)alloc_root(&alloc,max_key_len)) ||
      !(param.max_key= (uchar*)alloc_root(&alloc,max_key_len)))
  {
    thd->no_errors=0;
    free_root(&alloc,MYF(0));			// Return memory & allocator
    DBUG_RETURN(ERROR);
  }

  thd->mem_root= &alloc;
  /* Calculate cost of full index read for the shortest covering index */
  if (!force_quick_range && !head->covering_keys.is_clear_all() &&
      !head->no_keyread)
  {
    uint key_for_use= find_shortest_key(head, &head->covering_keys);
    double key_read_time= file->cost(file->
                                     ha_key_scan_and_compare_time(key_for_use,
                                                                  records));
    DBUG_PRINT("info",  ("'all'+'using index' scan will be using key %d, "
                         "read time %g", key_for_use, key_read_time));

    Json_writer_object trace_cov(thd, "best_covering_index_scan");
    bool chosen= FALSE;
    if (key_read_time < read_time)
    {
      read_time= key_read_time;
      chosen= TRUE;
    }
    if (unlikely(trace_cov.trace_started()))
    {
      trace_cov.
        add("index", head->key_info[key_for_use].name).
        add("cost", key_read_time).add("chosen", chosen);
      if (!chosen)
        trace_cov.add("cause", "cost");
    }
  }

  // Declared and initialized here as doing so later would skip goto jumps.
  SEL_ARG **backup_keys= nullptr;
  TABLE_READ_PLAN *best_read_plan= nullptr;
  double best_read_time= read_time;
  /*
    Set index_merge_allowed from OPTIMIZER_SWITCH_INDEX_MERGE.
    Notice also that OPTIMIZER_SWITCH_INDEX_MERGE disables all
    index merge sub strategies.
  */
  const bool index_merge_allowed =
      optimizer_flag(thd, OPTIMIZER_SWITCH_INDEX_MERGE);
  const bool index_merge_union_allowed =
      index_merge_allowed &&
      optimizer_flag(thd, OPTIMIZER_SWITCH_INDEX_MERGE_UNION);
  const bool index_merge_sort_union_allowed =
      index_merge_allowed &&
      optimizer_flag(thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION);

  if (notnull_cond)
    notnull_cond_tree= notnull_cond->get_mm_tree(&param, &notnull_cond);

  if (cond || notnull_cond_tree)
  {
    {
      Json_writer_array trace_range_summary(thd,
                                            "setup_range_conditions");
      if (cond)
        tree= cond->get_mm_tree(&param, &cond);
      if (notnull_cond_tree)
        tree= tree_and(&param, tree, notnull_cond_tree);
      if (thd->trace_started() &&
          param.alloced_sel_args >= thd->variables.optimizer_max_sel_args)
      {
        Json_writer_object wrapper(thd);
        Json_writer_object obj(thd, "sel_arg_alloc_limit_hit");
        obj.add("alloced_sel_args", param.alloced_sel_args);
      }
    }
    if (tree)
    {
      if (tree->type == SEL_TREE::IMPOSSIBLE)
      {
        records=0L;
        returnval= IMPOSSIBLE_RANGE;
        read_time= (double) HA_POS_ERROR;
        trace_range.add("impossible_range", true);
        goto free_mem;
      }
      /*
        If the tree can't be used for range scans, proceed anyway, as we
        can construct a group-min-max quick select
      */
      if (tree->type != SEL_TREE::KEY && tree->type != SEL_TREE::KEY_SMALLER)
      {
        trace_range.add("range_scan_possible", false);
        tree= nullptr;
      }
    }
    else if (thd->is_error())
    {
      thd->no_errors=0;
      thd->mem_root= param.old_root;
      free_root(&alloc, MYF(0));
      DBUG_RETURN(ERROR);
    }
  }

  if (tree)
  {
    /*
      It is possible to use a range-based quick select (but it might be
      slower than 'all' table scan).
    */
    Json_writer_object trace_range(thd, "analyzing_range_alternatives");

    backup_keys= (SEL_ARG**) alloca(sizeof(backup_keys[0])*param.keys);
    memcpy(&backup_keys[0], &tree->keys[0],
           sizeof(backup_keys[0])*param.keys);

    remove_nonrange_trees(&param, tree);

    /* Get best 'range' plan and prepare data for making other plans */
    TABLE_READ_PLAN *range_trp= nullptr;
    if ((range_trp= get_key_scans_params(&param, tree,
                                         only_single_index_range_scan,
                                         true, best_read_time, limit,
                                         1)))
    {
      best_read_plan= range_trp;
      best_read_time= best_read_plan->read_cost;
    }

    /*
      Simultaneous key scans and row deletes on several handler
      objects are not allowed so don't use ROR-intersection for
      table deletes.
    */
    TRP_ROR_INTERSECT *rori_trp= nullptr;
    if ((thd->lex->sql_command != SQLCOM_DELETE) &&
        (index_merge_allowed ||
         hint_table_state(thd, param.table->pos_in_table_list,
                          INDEX_MERGE_HINT_ENUM, 0)) &&
        !only_single_index_range_scan)
    {
      /*
        Get best non-covering ROR-intersection plan and prepare data for
        building covering ROR-intersection.
      */
      bool can_build_covering= FALSE;
      if ((rori_trp= get_best_ror_intersect(&param, tree, best_read_time,
                                            &can_build_covering, true)))
      {
        best_read_plan=       rori_trp;
        best_read_time= rori_trp->read_cost;
        /*
          Try constructing covering ROR-intersect only if it looks possible
          and worth doing.
        */
        if (!rori_trp->is_covering && can_build_covering &&
            (rori_trp= get_best_covering_ror_intersect(&param, tree,
                                                       best_read_time,
                                                       rori_trp->force_index_merge)))
          best_read_plan= rori_trp;
      }
    }
    /*
      Do not look for an index intersection  plan if there is a covering
      index. The scan by this covering index will be always cheaper than
      any index intersection.
    */
    if (param.table->covering_keys.is_clear_all() &&
        optimizer_flag(thd, OPTIMIZER_SWITCH_INDEX_MERGE) &&
        optimizer_flag(thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_INTERSECT) &&
        !only_single_index_range_scan)
    {
      TRP_INDEX_INTERSECT *intersect_trp= nullptr;
      if ((intersect_trp= get_best_index_intersect(&param, tree,
                                                  best_read_time)))
      {
        best_read_plan=       intersect_trp;
        best_read_time= intersect_trp->read_cost;
        param.table->set_opt_range_condition_rows(intersect_trp->records);
      }
    }

    TABLE_READ_PLAN *best_conj_trp= nullptr;
    if (!tree->merges.is_empty() &&
        (index_merge_allowed ||
         hint_table_state(thd, param.table->pos_in_table_list,
                          INDEX_MERGE_HINT_ENUM, 0)) &&
        table_records != 0 && !only_single_index_range_scan)
    {
      /* Try creating index_merge/ROR-union scan. */
      SEL_IMERGE *imerge;
      TABLE_READ_PLAN
        *UNINIT_VAR(new_conj_trp); /* no empty index_merge lists possible */
      DBUG_PRINT("info",("No range reads possible,"
                         " trying to construct index_merge"));
      List_iterator_fast<SEL_IMERGE> it(tree->merges);
      Json_writer_array trace_idx_merge(thd, "analyzing_index_merge_union");
      while ((imerge= it++))
      {
        new_conj_trp= get_best_disjunct_quick(&param,
                                              index_merge_union_allowed,
                                              index_merge_sort_union_allowed,
                                              imerge, best_read_time,
                                              limit, 0, 1);
        if (new_conj_trp)
          param.table->set_opt_range_condition_rows(new_conj_trp->records);
        if (new_conj_trp &&
            (!best_conj_trp ||
             new_conj_trp->read_cost < best_conj_trp->read_cost))
        {
          best_conj_trp= new_conj_trp;
          best_read_time= best_conj_trp->read_cost;
        }
      }
      if (best_conj_trp)
        best_read_plan= best_conj_trp;
    }
  }

  /*
    Try to construct a QUICK_GROUP_MIN_MAX_SELECT.
    Notice that it can be constructed no matter if there is a range tree.
  */
  DBUG_EXECUTE_IF("force_group_by", force_group_by = true; );
  if (!only_single_index_range_scan)
  {
    if (tree)
      restore_nonrange_trees(&param, tree, backup_keys);
    TRP_GROUP_MIN_MAX *group_trp= nullptr;
    if ((group_trp= get_best_group_min_max(&param, tree, read_time)))
    {
      /* mark that we are changing opt_range_condition_rows */
      group_by_optimization_used= 1;
      param.table->set_opt_range_condition_rows(group_trp->records);
      DBUG_PRINT("info", ("table_rows: %llu  opt_range_condition_rows: %llu  "
                          "group_trp->records: %llu",
                          table_records,
                          param.table->opt_range_condition_rows,
                          group_trp->records));

      Json_writer_object grp_summary(thd, "best_group_range_summary");

      if (unlikely(thd->trace_started()))
        group_trp->trace_basic_info(&param, &grp_summary);

      double duplicate_removal_cost= 0;
      if (group_trp->have_agg_distinct && group_trp->is_index_scan)
      {
        /*
          We are optimization a distinct aggregate, like
          SELECT count(DISTINCT a,b,c) FROM ...

          The group cost includes removal of the distinct, so to be
          able to compare costs, we add small cost to the original cost
          that stands for the extra work we have to do on the outside of
          the engine to do duplicate elimination for each output row if
          we are not using the grouping code.
        */
        duplicate_removal_cost= (DUPLICATE_REMOVAL_COST *
                                 (best_read_plan ? best_read_plan->records :
                                  table_records));
      }
      if (group_trp->read_cost < best_read_time + duplicate_removal_cost ||
          force_group_by)
      {
        if (thd->trace_started())
        {
          if (duplicate_removal_cost)
            grp_summary.add("duplicate_removal_cost", duplicate_removal_cost);
          grp_summary.add("chosen", true);
        }
        best_read_plan= group_trp;
      }
      else
        grp_summary.add("chosen", false).add("cause", "cost");
    }
    if (tree)
      remove_nonrange_trees(&param, tree);
  }

  thd->mem_root= param.old_root;

  /* If we got a read plan, create a quick select from it. */
  if (best_read_plan)
  {
    records= best_read_plan->records;
    if (records == 0)
      returnval= IMPOSSIBLE_RANGE;
    if (!(quick= best_read_plan->make_quick(&param, TRUE)) || quick->init())
    {
      delete quick;
      quick= nullptr;
    }
    else
    {
      quick->group_by_optimization_used= group_by_optimization_used;
      quick->force_index_merge= best_read_plan->force_index_merge;
    }
  }
  possible_keys= param.possible_keys;

free_mem:
  if (unlikely(quick && best_read_plan && thd->trace_started()))
  {
    Json_writer_object trace_range_summary(thd,
                                         "chosen_range_access_summary");
    {
      Json_writer_object trace_range_plan(thd, "range_access_plan");
      best_read_plan->trace_basic_info(&param, &trace_range_plan);
    }
    trace_range_summary.
      add("rows_for_plan", quick->records).
      add("cost_for_plan", quick->read_time).
      add("chosen", true);
  }

  free_root(&alloc,MYF(0));			// Return memory & allocator
  thd->mem_root= param.old_root;
  thd->no_errors=0;
  if (thd->killed || thd->is_error())
  {
    delete quick;
    quick= nullptr;
    returnval= ERROR;
  }

  DBUG_EXECUTE("info", print_quick(quick, &needed_reg););

  /*
    Assume that if the user is using 'limit' we will only need to scan
    limit rows if we are using a key
  */
  set_if_smaller(records, table_records);
  DBUG_RETURN(returnval);
}

/****************************************************************************
 * Condition selectivity module
 ****************************************************************************/


/*
  @brief
    Create a bitmap of columns for which to perform Range Analysis for EITS
    condition selectivity estimates.

  @detail
    Walk through the bitmap of fields used in the query, and
     - pick columns for which EITS data is usable (see is_eits_usable() call)
     - do not produce more than MAX_KEY columns. Range Analyzer cannot handle
       more than that. If there are more than MAX_KEY eligible columns,
       this function should be called multiple times to produce multiple
       bitmaps.

  @param  used_fields  Columns used by the query
  @param  col_no       Start from this column
  @param  out          OUT Filled column bitmap

  @return
     (uint)-1   If there are no more columns for range analysis.
     Other      Index of the last considered column. Pass this to next call to
                this function
*/

uint get_columns_for_pseudo_indexes(const TABLE *table,
                                    const MY_BITMAP *used_fields, int col_no,
                                    MY_BITMAP *out)
{
  bitmap_clear_all(out);
  int n_bits= 0;

  for (; table->field[col_no]; col_no++)
  {
    if (bitmap_is_set(used_fields, col_no) &&
        is_eits_usable(table->field[col_no]))
    {
      bitmap_set_bit(out, col_no);
      if (++n_bits == MAX_KEY)
      {
        col_no++;
        break;
      }
    }
  }
  return n_bits? col_no: (uint)-1;
}


/*
  Build descriptors of pseudo-indexes over columns to perform range analysis

  SYNOPSIS
    create_key_parts_for_pseudo_indexes()
      param       IN/OUT data structure for the descriptors to be built 
      used_fields bitmap of columns for which the descriptors are to be built

  DESCRIPTION
    For each column marked in the bitmap used_fields the function builds
    a descriptor of a single-component pseudo-index over this column that
    can be used for the range analysis of the predicates over this columns. 
    The descriptors are created in the memory of param->mem_root. 
   
  RETURN
    FALSE  in the case of success
    TRUE   otherwise
*/

static
bool create_key_parts_for_pseudo_indexes(RANGE_OPT_PARAM *param,
                                         MY_BITMAP *used_fields)
{
  Field **field_ptr;
  TABLE *table= param->table;
  uint parts= bitmap_bits_set(used_fields);

  KEY_PART *key_part;
  uint keys= 0;

  if (!(key_part= (KEY_PART *)  alloc_root(param->mem_root,
                                           sizeof(KEY_PART) * parts)))
    return TRUE;

  param->key_parts= key_part;
  uint max_key_len= 0;
  for (field_ptr= table->field; *field_ptr; field_ptr++)
  {
    Field *field= *field_ptr;
    if (bitmap_is_set(used_fields, field->field_index))
    {
      uint16 store_length;
      uint16 max_key_part_length= (uint16) table->file->max_key_part_length();
      key_part->key= keys;
      key_part->part= 0;
      if (field->flags & BLOB_FLAG)
        key_part->length= max_key_part_length;
      else
      {
        key_part->length= (uint16) field->key_length();
        set_if_smaller(key_part->length, max_key_part_length);
      }
      store_length= key_part->length;
      if (field->real_maybe_null())
        store_length+= HA_KEY_NULL_LENGTH;
      if (field->real_type() == MYSQL_TYPE_VARCHAR)
        store_length+= HA_KEY_BLOB_LENGTH;
      if (max_key_len < store_length)
        max_key_len= store_length;
      key_part->store_length= store_length; 
      key_part->field= field; 
      key_part->image_type= Field::itRAW;
      key_part->flag= 0;
      param->key[keys]= key_part;
      keys++;
      key_part++;
    }
  }

  max_key_len++; /* Take into account the "+1" in QUICK_RANGE::QUICK_RANGE */
  if (!(param->min_key= (uchar*)alloc_root(param->mem_root, max_key_len)) ||
      !(param->max_key= (uchar*)alloc_root(param->mem_root, max_key_len)))
  {
    return true;
  }
  param->keys= keys;
  param->key_parts_end= key_part;

  return FALSE;
}


/*
  Estimate the number of rows in all ranges built for a column
  by the range optimizer  

  SYNOPSIS
    records_in_column_ranges()
      param      the data structure to access descriptors of pseudo indexes
                 built over columns used in the condition of the processed
                 query
      idx        the index of the descriptor of interest in param
      tree       the tree representing ranges built for the interesting column

  DESCRIPTION
    This function retrieves the ranges represented by the SEL_ARG 'tree' and
    for each of them r it calls the function get_column_range_cardinality()
    that estimates the number of expected rows in r. It is assumed that param
    is the data structure containing the descriptors of pseudo-indexes that
    has been built to perform range analysis of the range conditions imposed
    on the columns used in the processed query, while idx is the index of the
    descriptor created in 'param' exactly for the column for which 'tree'
    has been built by the range optimizer.    

  RETURN
    the number of rows in the retrieved ranges  
*/

static
double records_in_column_ranges(PARAM *param, uint idx, 
                                SEL_ARG *tree)
{
  THD *thd= param->thd;
  SEL_ARG_RANGE_SEQ seq;
  KEY_MULTI_RANGE range;
  range_seq_t seq_it;
  double rows, table_records;
  Field *field;
  uint flags= 0;
  double total_rows= 0;
  RANGE_SEQ_IF seq_if = {NULL, sel_arg_range_seq_init, 
                         sel_arg_range_seq_next, 0, 0};
  
  /* Handle cases when we don't have a valid non-empty list of range */
  if (!tree)
    return DBL_MAX;
  if (tree->type == SEL_ARG::IMPOSSIBLE)
    return (0L);

  field= tree->field;

  seq.keyno= idx;
  seq.real_keyno= MAX_KEY;
  seq.key_parts= param->key[idx];
  seq.param= param;
  seq.start= tree;
  seq.is_ror_scan= FALSE;

  seq_it= seq_if.init((void *) &seq, 0, flags);

  Json_writer_array range_trace(thd, "ranges");

  while (!seq_if.next(seq_it, &range))
  {
    key_range *min_endp, *max_endp;
    min_endp= range.start_key.length? &range.start_key : NULL;
    max_endp= range.end_key.length? &range.end_key : NULL;
    int range_flag= range.range_flag;

    if (!range.start_key.length)
      range_flag |= NO_MIN_RANGE;
    if (!range.end_key.length)
      range_flag |= NO_MAX_RANGE;
    if (range.start_key.flag == HA_READ_AFTER_KEY)
      range_flag |= NEAR_MIN;
    if (range.start_key.flag == HA_READ_BEFORE_KEY)
      range_flag |= NEAR_MAX;

    if (unlikely(thd->trace_started()))
    {
      StringBuffer<128> range_info(system_charset_info);
      print_range_for_non_indexed_field(&range_info, field, &range);
      range_trace.add(range_info.c_ptr_safe(), range_info.length());
    }

    rows= get_column_range_cardinality(field, min_endp, max_endp, range_flag);
    if (DBL_MAX == rows)
    {
      total_rows= DBL_MAX;
      break;
    }
    total_rows+= rows;
  }
  if (total_rows == 0)
    total_rows= MY_MIN(1, rows2double(param->table->stat_records()));

  table_records= rows2double(param->table->stat_records());
  if (total_rows > table_records)
    DBUG_PRINT("error", ("table_records: %g < total_records: %g",
                         table_records, total_rows));
  return MY_MIN(total_rows, table_records);
}


/*
  Compare quick select ranges according to number of found rows
  If there is equal amounts of rows, use the long key part.
  The idea is that if we have keys (a),(a,b) and (a,b,c) and we have
  a query like WHERE a=1 and b=1 and c=1,
  it is better to use key (a,b,c) than (a) as it will ensure we don't also
  use histograms for columns b and c
*/

static int cmp_quick_ranges(const void *a_, const void *b_)
{
  const auto a= *static_cast<const TABLE::OPT_RANGE*const*>(a_);
  const auto b= *static_cast<const TABLE::OPT_RANGE*const*>(b_);
  if (int tmp= CMP_NUM(a->rows, b->rows))
    return tmp;
  return -CMP_NUM(a->key_parts, b->key_parts);
}


/*
  Calculate the selectivity of the condition imposed on the rows of a table

  SYNOPSIS
    calculate_cond_selectivity_for_table()
      thd        the context handle 
      table      the table of interest
      cond       conditions imposed on the rows of the table        

  DESCRIPTION
    This function calculates the selectivity of range conditions cond imposed
    on the rows of 'table' in the processed query.
    The calculated selectivity is assigned to the field
    table->cond_selectivity.
    
    Selectivity is calculated as a product of selectivities imposed by:

    1. possible range accesses. (if multiple range accesses use the same
       restrictions on the same field, we make adjustments for that)
    2. Sargable conditions on fields for which we have column statistics (if 
       a field is used in a possible range access, we assume that selectivity
       is already provided by the range access' estimates)
    3. Reading a few records from the table pages and checking the condition
       selectivity (this is used for conditions like "column LIKE '%val%'" 
       where approaches #1 and #2 do not provide selectivity data).
    4. If the selectivity calculated by get_best_ror_intersect() is smaller,
       use this instead.

  NOTE
    Currently the selectivities of range conditions over different columns are
    considered independent. 

  RETURN
    FALSE  on success
    TRUE   otherwise 
*/

bool calculate_cond_selectivity_for_table(THD *thd, TABLE *table, Item **cond)
{
  uint keynr, range_index, ranges;
  MY_BITMAP *used_fields= &table->cond_set;
  double table_records= (double)table->stat_records(), original_selectivity;
  TABLE::OPT_RANGE *optimal_key_order[MAX_KEY];
  MY_BITMAP handled_columns;
  my_bitmap_map *buf;
  QUICK_SELECT_I *quick;
  DBUG_ENTER("calculate_cond_selectivity_for_table");

  table->set_cond_selectivity(1.0);

  if (table_records == 0)
    DBUG_RETURN(FALSE);

  if ((quick=table->reginfo.join_tab->quick) &&
      quick->get_type() == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
  {
    DBUG_ASSERT(table->opt_range_condition_rows <= quick->records);
    table->set_cond_selectivity(MY_MIN(quick->records,
                                       table->opt_range_condition_rows)/
                                       table_records);
    DBUG_RETURN(FALSE);
  }

  if (!*cond || table->pos_in_table_list->schema_table)
  {
    table->set_cond_selectivity(table->opt_range_condition_rows /
                                table_records);
    DBUG_RETURN(FALSE);
  }

  /*
    This should be pre-alloced so that we could use the same bitmap for all
    tables. Would also avoid extra memory allocations if this function would
    be called multiple times per query.
  */
  if (!(buf= (my_bitmap_map*)thd->alloc(table->s->column_bitmap_size)))
    DBUG_RETURN(TRUE);
  my_bitmap_init(&handled_columns, buf, table->s->fields);

  /*
    Calculate the selectivity of the range conditions supported by indexes.

    First, take into account possible range accesses. 
    range access estimates are the most precise, we prefer them to any other
    estimate sources.
  */

  Json_writer_object trace_wrapper(thd);
  Json_writer_array selectivity_for_indexes(thd, "selectivity_for_indexes");

  /*
    Walk through all quick ranges in the order of least found rows.
  */
  for (ranges= keynr= 0 ; keynr < table->s->keys; keynr++)
    if (table->opt_range_keys.is_set(keynr))
      optimal_key_order[ranges++]= table->opt_range + keynr;

  my_qsort(optimal_key_order, ranges, sizeof *optimal_key_order,
           cmp_quick_ranges);

  for (range_index= 0 ; range_index < ranges ; range_index++)
  {
    TABLE::OPT_RANGE *range= optimal_key_order[range_index];
    uint keynr= (uint)(range - table->opt_range);
    uint i;
    uint used_key_parts= range->key_parts;
    double quick_cond_selectivity= (range->rows / table_records);
    KEY *key_info= table->key_info + keynr;
    KEY_PART_INFO* key_part= key_info->key_part;
    DBUG_ASSERT(quick_cond_selectivity <= 1.0);

    /*
      Suppose, there are range conditions on these keys
      KEY1 (col1, col2)
      KEY2 (col2, col6)
      KEY3 (col3, col2)
      KEY4 (col4, col5)

      We don't want to count selectivity for ranges that uses a column
      that was used before.
      If the first column of an index was not used before, we can use the
      key part statistics to calculate selectivity for this column. We cannot
      calculate statistics for any other columns as the key part statistics
      is also depending on the values of the previous key parts and not only
      the last key part.

      In other words, if KEY1 has the smallest range, we will only use first
      part of KEY3 and range of KEY4 to calculate selectivity.
    */
    for (i= 0; i < used_key_parts; i++)
    {
      if (bitmap_is_set(&handled_columns, key_part[i].fieldnr-1))
      {
        double rec_per_key;
        if (!i)
        {
          /*
            We cannot use this key part for selectivity calculation as
            key_info->actual_rec_per_key for later keys are depending on the
            distribution of the previous key parts.
          */
          goto end_of_range_loop;
        }
        /*
          A later key part was already used. We can still use key
          statistics for the first key part to get some approximation
          of the selectivity of this key. This can be done if the
          first key part is a constant:
          WHERE key1_part1=1 and key2_part1=5 and key2_part2 BETWEEN 0 and 10
          Even if key1 is used and it also includes the field for key2_part1
          as a key part, we can still use selectivity for key2_part1
        */
        if ((rec_per_key= key_info->actual_rec_per_key(0)) == 0.0 ||
            !range->first_key_part_has_only_one_value)
          goto end_of_range_loop;
        /*
          Use key distribution statistics, except if range selectivity
          is bigger. This can happen if the used key value has more
          than an average number of instances.
        */
        set_if_smaller(rec_per_key, rows2double(table->file->stats.records));
        set_if_bigger(quick_cond_selectivity,
                      rec_per_key / table->file->stats.records);
        used_key_parts= 1;
        break;
      }
    }
    /* Set bits only after we have checked the used columns */
    for (i= 0; i < used_key_parts; i++, key_part++)
      bitmap_set_bit(&handled_columns, key_part->fieldnr-1);

    /*
      There is at least 1-column prefix of columns whose selectivity has
      not yet been accounted for.
    */
    table->multiply_cond_selectivity(quick_cond_selectivity);

    if (unlikely(thd->trace_started()))
    {
      Json_writer_object selectivity_for_index(thd);
      selectivity_for_index.
        add("index_name", key_info->name).
        add("selectivity_from_index", quick_cond_selectivity);
    }
    /*
      We need to set selectivity for fields supported by indexes.
      For single-component indexes and for some first components
      of other indexes we do it here. For the remaining fields
      we do it later in this function, in the same way as for the
      fields not used in any indexes.
    */
    if (used_key_parts == 1)
    {
      uint fieldnr= key_info->key_part[0].fieldnr;
      table->field[fieldnr-1]->cond_selectivity= quick_cond_selectivity;
      DBUG_ASSERT(table->field[fieldnr-1]->cond_selectivity <= 1.0);
      /*
        Reset bit in used_fields to ensure this field is ignored in the loop
        below.
      */
      bitmap_clear_bit(used_fields, fieldnr-1);
    }
end_of_range_loop:
    continue;
  }
  /*
    Take into account number of matching rows calculated by
    get_best_ror_intersect() stored in table->opt_range_condition_rows
    Use the smaller found selectivity.
  */
  original_selectivity= (table->opt_range_condition_rows /
                         table_records);
  if (original_selectivity < table->cond_selectivity)
  {
    table->cond_selectivity= original_selectivity;
    if (unlikely(thd->trace_started()))
    {
      Json_writer_object selectivity_for_index(thd);
      selectivity_for_index.add("use_opt_range_condition_rows_selectivity",
                                original_selectivity);
    }
  }
  selectivity_for_indexes.end();
   
  /* 
    Second step: calculate the selectivity of the range conditions not 
    supported by any index and selectivity of the range condition
    over the fields whose selectivity has not been set yet.
  */
  Json_writer_array selectivity_for_columns(thd, "selectivity_for_columns");

  if (thd->variables.optimizer_use_condition_selectivity > 2 &&
      !bitmap_is_clear_all(used_fields) &&
      thd->variables.use_stat_tables > 0 && table->stats_is_read)
  {
    PARAM param;
    MEM_ROOT alloc;
    SEL_TREE *tree;
    init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                   thd->variables.range_alloc_block_size, 0,
                   MYF(MY_THREAD_SPECIFIC));
    bzero((void*) &param, sizeof(param));
    param.thd= thd;
    param.mem_root= &alloc;
    param.old_root= thd->mem_root;
    param.table= table;
    param.remove_false_where_parts= true;

    param.prev_tables= param.read_tables= 0;
    param.current_table= table->map;
    param.using_real_indexes= FALSE;
    MEM_UNDEFINED(&param.real_keynr, sizeof(param.real_keynr));

    param.alloced_sel_args= 0;
    param.max_key_parts= 0;

    thd->no_errors=1;
    table->reginfo.impossible_range= 0;

    uint used_fields_buff_size= bitmap_buffer_size(table->s->fields);
    my_bitmap_map *used_fields_buff= (my_bitmap_map*)thd->alloc(used_fields_buff_size);
    MY_BITMAP cols_for_indexes;
    (void) my_bitmap_init(&cols_for_indexes, used_fields_buff, table->s->fields);
    bitmap_clear_all(&cols_for_indexes);

    uint column_no= 0; // Start looping from the first column.
    /*
      Try getting selectivity estimates for every field that is used in the
      query and has EITS statistics. We do this:

        for every usable field col
           create a pseudo INDEX(col);
        Run the range analyzer (get_mm_tree) for these pseudo-indexes;
        Look at produced ranges and get their selectivity estimates;

      Note that the range analyzer can process at most MAX_KEY indexes. If
      the table has >MAX_KEY eligible columns, we will do several range
      analyzer runs.
    */

    while (1)
    {
      column_no= get_columns_for_pseudo_indexes(table, used_fields, column_no,
                                                &cols_for_indexes);
      if (column_no == (uint)-1)
        break;  /* Couldn't create any pseudo-indexes. This means we're done */

      if (create_key_parts_for_pseudo_indexes(&param, &cols_for_indexes))
        goto free_alloc;

      tree= cond[0]->get_mm_tree(&param, cond);

      if (!tree ||
          tree->type == SEL_TREE::ALWAYS ||
          tree->type == SEL_TREE::MAYBE)
      {
        /* Couldn't infer anything. But there could be more fields, so continue */
        continue;
      }

      if (tree->type == SEL_TREE::IMPOSSIBLE)
      {
        table->reginfo.impossible_range= 1;
        goto free_alloc;
      }

      for (uint idx= 0; idx < param.keys; idx++)
      {
        SEL_ARG *key= tree->keys[idx];
        if (key)
        {
          Json_writer_object selectivity_for_column(thd);
          selectivity_for_column.add("column_name", key->field->field_name);
          if (key->type == SEL_ARG::IMPOSSIBLE)
          {
            DBUG_ASSERT(key->field->cond_selectivity <= 1.0);
            table->reginfo.impossible_range= 1;
            if (unlikely(selectivity_for_column.trace_started()))
              selectivity_for_column.
                add("selectivity_from_histogram", 0).
                add("cause", "impossible range");
            goto free_alloc;
          }
          else
          {
            enum_check_fields save_count_cuted_fields= thd->count_cuted_fields;
            thd->count_cuted_fields= CHECK_FIELD_IGNORE;
            double rows= records_in_column_ranges(&param, idx, key);
            thd->count_cuted_fields= save_count_cuted_fields;
            if (rows != DBL_MAX)
            {
              key->field->cond_selectivity= rows/table_records;
              selectivity_for_column.add("selectivity_from_histogram",
                                         key->field->cond_selectivity);
            }
          }
        }
      }
    }

    for (Field **field_ptr= table->field; *field_ptr; field_ptr++)
    {
      Field *table_field= *field_ptr;   
      if (bitmap_is_set(used_fields, table_field->field_index) &&
          table_field->cond_selectivity < 1.0)
      {
        if (!bitmap_is_set(&handled_columns, table_field->field_index))
          table->multiply_cond_selectivity(table_field->cond_selectivity);
      }
    }

  free_alloc:
    thd->no_errors= 0;
    thd->mem_root= param.old_root;
    free_root(&alloc, MYF(0));

  }
  selectivity_for_columns.end();

  bitmap_union(used_fields, &handled_columns);

  /* Check if we can improve selectivity estimates by using sampling */
  ulong check_rows=
    MY_MIN(thd->variables.optimizer_selectivity_sampling_limit,
        (ulong) (table_records * SELECTIVITY_SAMPLING_SHARE));
  if (*cond && check_rows > SELECTIVITY_SAMPLING_THRESHOLD &&
      thd->variables.optimizer_use_condition_selectivity > 4)
  {
    Json_writer_array trace_sampled_sel(thd, "sampled_selectivity");
    find_selective_predicates_list_processor_data *dt=
      (find_selective_predicates_list_processor_data *)
      alloc_root(thd->mem_root,
                 sizeof(find_selective_predicates_list_processor_data));
    if (!dt)
      DBUG_RETURN(TRUE);
    dt->list.empty();
    dt->table= table;
    if ((*cond)->walk(&Item::find_selective_predicates_list_processor, dt, 0))
      DBUG_RETURN(TRUE);
    if (dt->list.elements > 0)
    {
      check_rows= check_selectivity(thd, check_rows, table, &dt->list);
      if (check_rows > SELECTIVITY_SAMPLING_THRESHOLD)
      {
        COND_STATISTIC *stat;
        List_iterator_fast<COND_STATISTIC> it(dt->list);
        double examined_rows= check_rows;
        while ((stat= it++))
        {
          if (!stat->positive)
          {
            DBUG_PRINT("info", ("To avoid 0 assigned 1 to the counter"));
            stat->positive= 1; // avoid 0
          }
          DBUG_PRINT("info", ("The predicate selectivity : %g",
                              (double)stat->positive / examined_rows));
          double selectivity= ((double)stat->positive) / examined_rows;
          table->multiply_cond_selectivity(selectivity);

          if (unlikely(trace_sampled_sel.trace_started()))
          {
            Json_writer_object selectivity_for_cond(thd);
            selectivity_for_cond.add("cond", stat->cond);
            selectivity_for_cond.add("selectivity", selectivity);
          }
          /*
            If a field is involved then we register its selectivity in case
            there in an equality with the field.
            For example in case
            t1.a LIKE "%bla%" and t1.a = t2.b
            the selectivity we have found could be used also for t2.
          */
          if (stat->field_arg)
          {
            stat->field_arg->cond_selectivity*= selectivity;

            if (stat->field_arg->next_equal_field)
            {
              for (Field *next_field= stat->field_arg->next_equal_field;
                   next_field != stat->field_arg;
                   next_field= next_field->next_equal_field)
              {
                next_field->cond_selectivity*= selectivity;
                next_field->table->cond_selectivity*= selectivity;
              }
            }
          }
        }

      }
      /* This list and its elements put to mem_root so should not be freed */
      table->cond_selectivity_sampling_explain= &dt->list;
    }
  }
  trace_wrapper.add("cond_selectivity", table->cond_selectivity);
  DBUG_RETURN(FALSE);
}

/****************************************************************************
 * Condition selectivity code ends
 ****************************************************************************/

/****************************************************************************
 * Partition pruning module
 ****************************************************************************/

/*
  Store field key image to table record

  SYNOPSIS
    store_key_image_to_rec()
      field  Field which key image should be stored
      ptr    Field value in key format
      len    Length of the value, in bytes
  
  ATTENTION
    len is the length of the value not counting the NULL-byte (at the same
    time, ptr points to the key image, which starts with NULL-byte for 
    nullable columns)

  DESCRIPTION
    Copy the field value from its key image to the table record. The source
    is the value in key image format, occupying len bytes in buffer pointed
    by ptr. The destination is table record, in "field value in table record"
    format.
*/

void store_key_image_to_rec(Field *field, uchar *ptr, uint len)
{
  /* Do the same as print_key() does */

  if (field->real_maybe_null())
  {
    if (*ptr)
    {
      field->set_null();
      return;
    }
    field->set_notnull();
    ptr++;
  }    
  MY_BITMAP *old_map= dbug_tmp_use_all_columns(field->table,
                                    &field->table->write_set);
  field->set_key_image(ptr, len); 
  dbug_tmp_restore_column_map(&field->table->write_set, old_map);
}

#ifdef WITH_PARTITION_STORAGE_ENGINE

/*
  PartitionPruningModule

  This part of the code does partition pruning. Partition pruning solves the
  following problem: given a query over partitioned tables, find partitions
  that we will not need to access (i.e. partitions that we can assume to be
  empty) when executing the query.
  The set of partitions to prune doesn't depend on which query execution
  plan will be used to execute the query.
  
  HOW IT WORKS
  
  Partition pruning module makes use of RangeAnalysisModule. The following
  examples show how the problem of partition pruning can be reduced to the 
  range analysis problem:
  
  EXAMPLE 1
    Consider a query:
    
      SELECT * FROM t1 WHERE (t1.a < 5 OR t1.a = 10) AND t1.a > 3 AND t1.b='z'
    
    where table t1 is partitioned using PARTITION BY RANGE(t1.a).  An apparent
    way to find the used (i.e. not pruned away) partitions is as follows:
    
    1. analyze the WHERE clause and extract the list of intervals over t1.a
       for the above query we will get this list: {(3 < t1.a < 5), (t1.a=10)}

    2. for each interval I
       {
         find partitions that have non-empty intersection with I;
         mark them as used;
       }
       
  EXAMPLE 2
    Suppose the table is partitioned by HASH(part_func(t1.a, t1.b)). Then
    we need to:

    1. Analyze the WHERE clause and get a list of intervals over (t1.a, t1.b).
       The list of intervals we'll obtain will look like this:
       ((t1.a, t1.b) = (1,'foo')),
       ((t1.a, t1.b) = (2,'bar')), 
       ((t1,a, t1.b) > (10,'zz'))
       
    2. for each interval I 
       {
         if (the interval has form "(t1.a, t1.b) = (const1, const2)" )
         {
           calculate HASH(part_func(t1.a, t1.b));
           find which partition has records with this hash value and mark
             it as used;
         }
         else
         {
           mark all partitions as used; 
           break;
         }
       }

   For both examples the step #1 is exactly what RangeAnalysisModule could
   be used to do, if it was provided with appropriate index description
   (array of KEY_PART structures). 
   In example #1, we need to provide it with description of index(t1.a), 
   in example #2, we need to provide it with description of index(t1.a, t1.b).
   
   These index descriptions are further called "partitioning index
   descriptions". Note that it doesn't matter if such indexes really exist,
   as range analysis module only uses the description.
   
   Putting it all together, partitioning module works as follows:
   
   prune_partitions() {
     call create_partition_index_description();

     call get_mm_tree(); // invoke the RangeAnalysisModule
     
     // analyze the obtained interval list and get used partitions 
     call find_used_partitions();
  }

*/

struct st_part_prune_param;
struct st_part_opt_info;

typedef void (*mark_full_part_func)(partition_info*, uint32);

/*
  Partition pruning operation context
*/
typedef struct st_part_prune_param
{
  RANGE_OPT_PARAM range_param; /* Range analyzer parameters */

  /***************************************************************
   Following fields are filled in based solely on partitioning 
   definition and not modified after that:
   **************************************************************/
  partition_info *part_info; /* Copy of table->part_info */
  /* Function to get partition id from partitioning fields only */
  get_part_id_func get_top_partition_id_func;
  /* Function to mark a partition as used (w/all subpartitions if they exist)*/
  mark_full_part_func mark_full_partition_used;
 
  /* Partitioning 'index' description, array of key parts */
  KEY_PART *key;
  
  /*
    Number of fields in partitioning 'index' definition created for
    partitioning (0 if partitioning 'index' doesn't include partitioning
    fields)
  */
  uint part_fields;
  uint subpart_fields; /* Same as above for subpartitioning */
  
  /* 
    Number of the last partitioning field keypart in the index, or -1 if
    partitioning index definition doesn't include partitioning fields.
  */
  int last_part_partno;
  int last_subpart_partno; /* Same as above for subpartitioning */

  /*
    is_part_keypart[i] == MY_TEST(keypart #i in partitioning index is a member
                                  used in partitioning)
    Used to maintain current values of cur_part_fields and cur_subpart_fields
  */
  my_bool *is_part_keypart;
  /* Same as above for subpartitioning */
  my_bool *is_subpart_keypart;

  my_bool ignore_part_fields; /* Ignore rest of partitioning fields */

  /***************************************************************
   Following fields form find_used_partitions() recursion context:
   **************************************************************/
  SEL_ARG **arg_stack;     /* "Stack" of SEL_ARGs */
  SEL_ARG **arg_stack_end; /* Top of the stack    */
  /* Number of partitioning fields for which we have a SEL_ARG* in arg_stack */
  uint cur_part_fields;
  /* Same as cur_part_fields, but for subpartitioning */
  uint cur_subpart_fields;

  /* Iterator to be used to obtain the "current" set of used partitions */
  PARTITION_ITERATOR part_iter;

  /* Initialized bitmap of num_subparts size */
  MY_BITMAP subparts_bitmap;

  uchar *cur_min_key;
  uchar *cur_max_key;

  uint cur_min_flag, cur_max_flag;
} PART_PRUNE_PARAM;

static bool create_partition_index_description(PART_PRUNE_PARAM *prune_par);
static int find_used_partitions(PART_PRUNE_PARAM *ppar, SEL_ARG *key_tree);
static int find_used_partitions_imerge(PART_PRUNE_PARAM *ppar,
                                       SEL_IMERGE *imerge);
static int find_used_partitions_imerge_list(PART_PRUNE_PARAM *ppar,
                                            List<SEL_IMERGE> &merges);
static void mark_all_partitions_as_used(partition_info *part_info);

#ifndef DBUG_OFF
static void print_partitioning_index(KEY_PART *parts, KEY_PART *parts_end);
static void dbug_print_field(Field *field);
static void dbug_print_segment_range(SEL_ARG *arg, KEY_PART *part);
static void dbug_print_singlepoint_range(SEL_ARG **start, uint num);
#endif


/**
  Perform partition pruning for a given table and condition.

  @param      thd            Thread handle
  @param      table          Table to perform partition pruning for
  @param      pprune_cond    Condition to use for partition pruning
  
  @note This function assumes that lock_partitions are setup when it
  is invoked. The function analyzes the condition, finds partitions that
  need to be used to retrieve the records that match the condition, and 
  marks them as used by setting appropriate bit in part_info->read_partitions
  In the worst case all partitions are marked as used. If the table is not
  yet locked, it will also unset bits in part_info->lock_partitions that is
  not set in read_partitions.

  This function returns promptly if called for non-partitioned table.

  @return Operation status
    @retval true  Failure
    @retval false Success
*/

bool prune_partitions(THD *thd, TABLE *table, Item *pprune_cond)
{
  bool retval= FALSE;
  partition_info *part_info = table->part_info;
  DBUG_ENTER("prune_partitions");

  if (!part_info)
    DBUG_RETURN(FALSE); /* not a partitioned table */
  
  if (!pprune_cond)
  {
    mark_all_partitions_as_used(part_info);
    DBUG_RETURN(FALSE);
  }
  
  PART_PRUNE_PARAM prune_param;
  MEM_ROOT alloc;
  RANGE_OPT_PARAM  *range_par= &prune_param.range_param;
  MY_BITMAP *old_sets[2];

  prune_param.part_info= part_info;
  init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                 thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
  bzero((void*) range_par, sizeof(*range_par));
  range_par->mem_root= &alloc;
  range_par->old_root= thd->mem_root;

  if (create_partition_index_description(&prune_param))
  {
    mark_all_partitions_as_used(part_info);
    free_root(&alloc,MYF(0));		// Return memory & allocator
    DBUG_RETURN(FALSE);
  }

  dbug_tmp_use_all_columns(table, old_sets, 
                           &table->read_set, &table->write_set);
  range_par->thd= thd;
  range_par->table= table;
  /* range_par->cond doesn't need initialization */
  range_par->prev_tables= range_par->read_tables= 0;
  range_par->current_table= table->map;
  /* It should be possible to switch the following ON: */
  range_par->remove_false_where_parts= false;

  range_par->keys= 1; // one index
  range_par->using_real_indexes= FALSE;
  range_par->remove_jump_scans= FALSE;
  range_par->real_keynr[0]= 0;
  range_par->alloced_sel_args= 0;
  range_par->note_unusable_keys= Item_func::BITMAP_NONE;

  thd->no_errors=1;				// Don't warn about NULL
  thd->mem_root=&alloc;

  bitmap_clear_all(&part_info->read_partitions);

  prune_param.key= prune_param.range_param.key_parts;
  SEL_TREE *tree;
  int res;

  tree= pprune_cond->get_mm_tree(range_par, &pprune_cond);
  if (!tree)
    goto all_used;

  if (tree->type == SEL_TREE::IMPOSSIBLE)
  {
    retval= TRUE;
    goto end;
  }

  if (tree->type != SEL_TREE::KEY && tree->type != SEL_TREE::KEY_SMALLER)
    goto all_used;

  if (tree->merges.is_empty())
  {
    /* Range analysis has produced a single list of intervals. */
    prune_param.arg_stack_end= prune_param.arg_stack;
    prune_param.cur_part_fields= 0;
    prune_param.cur_subpart_fields= 0;
    
    prune_param.cur_min_key= prune_param.range_param.min_key;
    prune_param.cur_max_key= prune_param.range_param.max_key;
    prune_param.cur_min_flag= prune_param.cur_max_flag= 0;

    init_all_partitions_iterator(part_info, &prune_param.part_iter);
    if (!tree->keys[0] || (-1 == (res= find_used_partitions(&prune_param,
                                                            tree->keys[0]))))
      goto all_used;
  }
  else
  {
    if (tree->merges.elements == 1)
    {
      /* 
        Range analysis has produced a "merge" of several intervals lists, a 
        SEL_TREE that represents an expression in form         
          sel_imerge = (tree1 OR tree2 OR ... OR treeN)
        that cannot be reduced to one tree. This can only happen when 
        partitioning index has several keyparts and the condition is OR of
        conditions that refer to different key parts. For example, we'll get
        here for "partitioning_field=const1 OR subpartitioning_field=const2"
      */
      if (-1 == (res= find_used_partitions_imerge(&prune_param,
                                                  tree->merges.head())))
        goto all_used;
    }
    else
    {
      /* 
        Range analysis has produced a list of several imerges, i.e. a
        structure that represents a condition in form 
        imerge_list= (sel_imerge1 AND sel_imerge2 AND ... AND sel_imergeN)
        This is produced for complicated WHERE clauses that range analyzer
        can't really analyze properly.
      */
      if (-1 == (res= find_used_partitions_imerge_list(&prune_param,
                                                       tree->merges)))
        goto all_used;
    }
  }
  
  /*
    res == 0 => no used partitions => retval=TRUE
    res == 1 => some used partitions => retval=FALSE
    res == -1 - we jump over this line to all_used:
  */
  retval= MY_TEST(!res);
  goto end;

all_used:
  retval= FALSE; // some partitions are used
  mark_all_partitions_as_used(prune_param.part_info);
end:
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);
  thd->no_errors=0;
  thd->mem_root= range_par->old_root;
  free_root(&alloc,MYF(0));			// Return memory & allocator
  /*
    Must be a subset of the locked partitions.
    lock_partitions contains the partitions marked by explicit partition
    selection (... t PARTITION (pX) ...) and we must only use partitions
    within that set.
  */
  bitmap_intersect(&prune_param.part_info->read_partitions,
                   &prune_param.part_info->lock_partitions);
  /*
    If not yet locked, also prune partitions to lock if not UPDATEing
    partition key fields. This will also prune lock_partitions if we are under
    LOCK TABLES, so prune away calls to start_stmt().
    TODO: enhance this prune locking to also allow pruning of
    'UPDATE t SET part_key = const WHERE cond_is_prunable' so it adds
    a lock for part_key partition.
  */
  if (table->file->get_lock_type() == F_UNLCK &&
      !partition_key_modified(table, table->write_set))
  {
    bitmap_copy(&prune_param.part_info->lock_partitions,
                &prune_param.part_info->read_partitions);
  }
  if (bitmap_is_clear_all(&(prune_param.part_info->read_partitions)))
  {
    table->all_partitions_pruned_away= true;
    retval= TRUE;
  }

  if (unlikely(thd->trace_started()))
  {
    String parts;
    String_list parts_list;

    make_used_partitions_str(thd->mem_root, prune_param.part_info, &parts,
                               parts_list);
    Json_writer_object trace_wrapper(thd);
    Json_writer_object trace_prune(thd, "prune_partitions");
    trace_prune.add_table_name(table);
    trace_prune.add("used_partitions", parts.c_ptr());
  }

  DBUG_RETURN(retval);
}


/*
  For SEL_ARG* array, store sel_arg->min values into table record buffer

  SYNOPSIS
    store_selargs_to_rec()
      ppar   Partition pruning context
      start  Array of SEL_ARG* for which the minimum values should be stored
      num    Number of elements in the array

  DESCRIPTION
    For each SEL_ARG* interval in the specified array, store the left edge
    field value (sel_arg->min, key image format) into the table record.
*/

static void store_selargs_to_rec(PART_PRUNE_PARAM *ppar, SEL_ARG **start,
                                 int num)
{
  KEY_PART *parts= ppar->range_param.key_parts;
  for (SEL_ARG **end= start + num; start != end; start++)
  {
    SEL_ARG *sel_arg= (*start);
    store_key_image_to_rec(sel_arg->field, sel_arg->min_value,
                           parts[sel_arg->part].length);
  }
}


/* Mark a partition as used in the case when there are no subpartitions */
static void mark_full_partition_used_no_parts(partition_info* part_info,
                                              uint32 part_id)
{
  DBUG_ENTER("mark_full_partition_used_no_parts");
  DBUG_PRINT("enter", ("Mark partition %u as used", part_id));
  bitmap_set_bit(&part_info->read_partitions, part_id);
  DBUG_VOID_RETURN;
}


/* Mark a partition as used in the case when there are subpartitions */
static void mark_full_partition_used_with_parts(partition_info *part_info,
                                                uint32 part_id)
{
  uint32 start= part_id * part_info->num_subparts;
  uint32 end=   start + part_info->num_subparts; 
  DBUG_ENTER("mark_full_partition_used_with_parts");

  for (; start != end; start++)
  {
    DBUG_PRINT("info", ("1:Mark subpartition %u as used", start));
    bitmap_set_bit(&part_info->read_partitions, start);
  }
  DBUG_VOID_RETURN;
}

/*
  Find the set of used partitions for List<SEL_IMERGE>
  SYNOPSIS
    find_used_partitions_imerge_list
      ppar      Partition pruning context.
      key_tree  Intervals tree to perform pruning for.
      
  DESCRIPTION
    List<SEL_IMERGE> represents "imerge1 AND imerge2 AND ...". 
    The set of used partitions is an intersection of used partitions sets
    for imerge_{i}.
    We accumulate this intersection in a separate bitmap.
 
  RETURN 
    See find_used_partitions()
*/

static int find_used_partitions_imerge_list(PART_PRUNE_PARAM *ppar,
                                            List<SEL_IMERGE> &merges)
{
  MY_BITMAP all_merges;
  uint bitmap_bytes;
  my_bitmap_map *bitmap_buf;
  uint n_bits= ppar->part_info->read_partitions.n_bits;
  bitmap_bytes= bitmap_buffer_size(n_bits);
  if (!(bitmap_buf= (my_bitmap_map*) alloc_root(ppar->range_param.mem_root,
                                                bitmap_bytes)))
  {
    /*
      Fallback, process just the first SEL_IMERGE. This can leave us with more
      partitions marked as used then actually needed.
    */
    return find_used_partitions_imerge(ppar, merges.head());
  }
  my_bitmap_init(&all_merges, bitmap_buf, n_bits);
  bitmap_set_prefix(&all_merges, n_bits);

  List_iterator<SEL_IMERGE> it(merges);
  SEL_IMERGE *imerge;
  while ((imerge=it++))
  {
    int res= find_used_partitions_imerge(ppar, imerge);
    if (!res)
    {
      /* no used partitions on one ANDed imerge => no used partitions at all */
      return 0;
    }

    if (res != -1)
      bitmap_intersect(&all_merges, &ppar->part_info->read_partitions);


    if (bitmap_is_clear_all(&all_merges))
      return 0;

    bitmap_clear_all(&ppar->part_info->read_partitions);
  }
  memcpy(ppar->part_info->read_partitions.bitmap, all_merges.bitmap,
         bitmap_bytes);
  return 1;
}


/*
  Find the set of used partitions for SEL_IMERGE structure
  SYNOPSIS
    find_used_partitions_imerge()
      ppar      Partition pruning context.
      key_tree  Intervals tree to perform pruning for.
      
  DESCRIPTION
    SEL_IMERGE represents "tree1 OR tree2 OR ...". The implementation is
    trivial - just use mark used partitions for each tree and bail out early
    if for some tree_{i} all partitions are used.
 
  RETURN 
    See find_used_partitions().
*/

static
int find_used_partitions_imerge(PART_PRUNE_PARAM *ppar, SEL_IMERGE *imerge)
{
  int res= 0;
  for (SEL_TREE **ptree= imerge->trees; ptree < imerge->trees_next; ptree++)
  {
    ppar->arg_stack_end= ppar->arg_stack;
    ppar->cur_part_fields= 0;
    ppar->cur_subpart_fields= 0;
    
    ppar->cur_min_key= ppar->range_param.min_key;
    ppar->cur_max_key= ppar->range_param.max_key;
    ppar->cur_min_flag= ppar->cur_max_flag= 0;

    init_all_partitions_iterator(ppar->part_info, &ppar->part_iter);
    SEL_ARG *key_tree= (*ptree)->keys[0];
    if (!key_tree || (-1 == (res |= find_used_partitions(ppar, key_tree))))
      return -1;
  }
  return res;
}


/*
  Collect partitioning ranges for the SEL_ARG tree and mark partitions as used

  SYNOPSIS
    find_used_partitions()
      ppar      Partition pruning context.
      key_tree  SEL_ARG range tree to perform pruning for

  DESCRIPTION
    This function 
      * recursively walks the SEL_ARG* tree collecting partitioning "intervals"
      * finds the partitions one needs to use to get rows in these intervals
      * marks these partitions as used.
    The next session desribes the process in greater detail.
 
  IMPLEMENTATION
    TYPES OF RESTRICTIONS THAT WE CAN OBTAIN PARTITIONS FOR    
    We can find out which [sub]partitions to use if we obtain restrictions on 
    [sub]partitioning fields in the following form:
    1.  "partition_field1=const1 AND ... AND partition_fieldN=constN"
    1.1  Same as (1) but for subpartition fields

    If partitioning supports interval analysis (i.e. partitioning is a
    function of a single table field, and partition_info::
    get_part_iter_for_interval != NULL), then we can also use condition in
    this form:
    2.  "const1 <=? partition_field <=? const2"
    2.1  Same as (2) but for subpartition_field

    INFERRING THE RESTRICTIONS FROM SEL_ARG TREE
    
    The below is an example of what SEL_ARG tree may represent:
    
    (start)
     |                           $
     |   Partitioning keyparts   $  subpartitioning keyparts
     |                           $
     |     ...          ...      $
     |      |            |       $
     | +---------+  +---------+  $  +-----------+  +-----------+
     \-| par1=c1 |--| par2=c2 |-----| subpar1=c3|--| subpar2=c5|
       +---------+  +---------+  $  +-----------+  +-----------+
            |                    $        |             |
            |                    $        |        +-----------+ 
            |                    $        |        | subpar2=c6|
            |                    $        |        +-----------+ 
            |                    $        |
            |                    $  +-----------+  +-----------+
            |                    $  | subpar1=c4|--| subpar2=c8|
            |                    $  +-----------+  +-----------+
            |                    $         
            |                    $
       +---------+               $  +------------+  +------------+
       | par1=c2 |------------------| subpar1=c10|--| subpar2=c12|
       +---------+               $  +------------+  +------------+
            |                    $
           ...                   $

    The up-down connections are connections via SEL_ARG::left and
    SEL_ARG::right. A horizontal connection to the right is the
    SEL_ARG::next_key_part connection.
    
    find_used_partitions() traverses the entire tree via recursion on
     * SEL_ARG::next_key_part (from left to right on the picture)
     * SEL_ARG::left|right (up/down on the pic). Left-right recursion is
       performed for each depth level.
    
    Recursion descent on SEL_ARG::next_key_part is used to accumulate (in
    ppar->arg_stack) constraints on partitioning and subpartitioning fields.
    For the example in the above picture, one of stack states is:
      in find_used_partitions(key_tree = "subpar2=c5") (***)
      in find_used_partitions(key_tree = "subpar1=c3")
      in find_used_partitions(key_tree = "par2=c2")   (**)
      in find_used_partitions(key_tree = "par1=c1")
      in prune_partitions(...)
    We apply partitioning limits as soon as possible, e.g. when we reach the
    depth (**), we find which partition(s) correspond to "par1=c1 AND par2=c2",
    and save them in ppar->part_iter.
    When we reach the depth (***), we find which subpartition(s) correspond to
    "subpar1=c3 AND subpar2=c5", and then mark appropriate subpartitions in
    appropriate subpartitions as used.
    
    It is possible that constraints on some partitioning fields are missing.
    For the above example, consider this stack state:
      in find_used_partitions(key_tree = "subpar2=c12") (***)
      in find_used_partitions(key_tree = "subpar1=c10")
      in find_used_partitions(key_tree = "par1=c2")
      in prune_partitions(...)
    Here we don't have constraints for all partitioning fields. Since we've
    never set the ppar->part_iter to contain used set of partitions, we use
    its default "all partitions" value.  We get  subpartition id for 
    "subpar1=c3 AND subpar2=c5", and mark that subpartition as used in every
    partition.

    The inverse is also possible: we may get constraints on partitioning
    fields, but not constraints on subpartitioning fields. In that case,
    calls to find_used_partitions() with depth below (**) will return -1,
    and we will mark entire partition as used.

  TODO
    Replace recursion on SEL_ARG::left and SEL_ARG::right with a loop

  RETURN
    1   OK, one or more [sub]partitions are marked as used.
    0   The passed condition doesn't match any partitions
   -1   Couldn't infer any partition pruning "intervals" from the passed 
        SEL_ARG* tree (which means that all partitions should be marked as
        used) Marking partitions as used is the responsibility of the caller.
*/

static 
int find_used_partitions(PART_PRUNE_PARAM *ppar, SEL_ARG *key_tree)
{
  int res, left_res=0, right_res=0;
  int key_tree_part= (int)key_tree->part;
  bool set_full_part_if_bad_ret= FALSE;
  bool ignore_part_fields= ppar->ignore_part_fields;
  bool did_set_ignore_part_fields= FALSE;
  RANGE_OPT_PARAM *range_par= &(ppar->range_param);

  if (check_stack_overrun(range_par->thd, 3*STACK_MIN_SIZE, NULL))
    return -1;

  if (key_tree->left != &null_element)
  {
    if (-1 == (left_res= find_used_partitions(ppar,key_tree->left)))
      return -1;
  }

  /* Push SEL_ARG's to stack to enable looking backwards as well */
  ppar->cur_part_fields+= ppar->is_part_keypart[key_tree_part];
  ppar->cur_subpart_fields+= ppar->is_subpart_keypart[key_tree_part];
  *(ppar->arg_stack_end++)= key_tree;

  if (ignore_part_fields)
  {
    /*
      We come here when a condition on the first partitioning
      fields led to evaluating the partitioning condition
      (due to finding a condition of the type a < const or
      b > const). Thus we must ignore the rest of the
      partitioning fields but we still want to analyse the
      subpartitioning fields.
    */
    if (key_tree->next_key_part)
      res= find_used_partitions(ppar, key_tree->next_key_part);
    else
      res= -1;
    goto pop_and_go_right;
  }

  if (key_tree->type == SEL_ARG::KEY_RANGE)
  {
    if (ppar->part_info->get_part_iter_for_interval && 
        key_tree->part <= ppar->last_part_partno)
    {
      /* Collect left and right bound, their lengths and flags */
      uchar *min_key= ppar->cur_min_key;
      uchar *max_key= ppar->cur_max_key;
      uchar *tmp_min_key= min_key;
      uchar *tmp_max_key= max_key;
      key_tree->store_min(ppar->key[key_tree->part].store_length,
                          &tmp_min_key, ppar->cur_min_flag);
      key_tree->store_max(ppar->key[key_tree->part].store_length,
                          &tmp_max_key, ppar->cur_max_flag);
      uint flag;
      if (key_tree->next_key_part &&
          key_tree->next_key_part->part == key_tree->part+1 &&
          key_tree->next_key_part->part <= ppar->last_part_partno &&
          key_tree->next_key_part->type == SEL_ARG::KEY_RANGE)
      {
        /*
          There are more key parts for partition pruning to handle
          This mainly happens when the condition is an equality
          condition.
        */
        if ((tmp_min_key - min_key) == (tmp_max_key - max_key) && 
            (memcmp(min_key, max_key, (uint)(tmp_max_key - max_key)) == 0) &&
            !key_tree->min_flag && !key_tree->max_flag)
        {
          /* Set 'parameters' */
          ppar->cur_min_key= tmp_min_key;
          ppar->cur_max_key= tmp_max_key;
          uint save_min_flag= ppar->cur_min_flag;
          uint save_max_flag= ppar->cur_max_flag;

          ppar->cur_min_flag|= key_tree->min_flag;
          ppar->cur_max_flag|= key_tree->max_flag;
          
          res= find_used_partitions(ppar, key_tree->next_key_part);
           
          /* Restore 'parameters' back */
          ppar->cur_min_key= min_key;
          ppar->cur_max_key= max_key;

          ppar->cur_min_flag= save_min_flag;
          ppar->cur_max_flag= save_max_flag;
          goto pop_and_go_right;
        }
        /* We have arrived at the last field in the partition pruning */
        uint tmp_min_flag= key_tree->min_flag,
             tmp_max_flag= key_tree->max_flag;
        if (!tmp_min_flag)
          key_tree->next_key_part->store_min_key(ppar->key,
                                                 &tmp_min_key,
                                                 &tmp_min_flag,
                                                 ppar->last_part_partno,
                                                 true);
        if (!tmp_max_flag)
          key_tree->next_key_part->store_max_key(ppar->key,
                                                 &tmp_max_key,
                                                 &tmp_max_flag,
                                                 ppar->last_part_partno,
                                                 false);
        flag= tmp_min_flag | tmp_max_flag;
      }
      else
        flag= key_tree->min_flag | key_tree->max_flag;
      
      if (tmp_min_key != range_par->min_key)
        flag&= ~NO_MIN_RANGE;
      else
        flag|= NO_MIN_RANGE;
      if (tmp_max_key != range_par->max_key)
        flag&= ~NO_MAX_RANGE;
      else
        flag|= NO_MAX_RANGE;

      /*
        We need to call the interval mapper if we have a condition which
        makes sense to prune on. In the example of COLUMNS on a and
        b it makes sense if we have a condition on a, or conditions on
        both a and b. If we only have conditions on b it might make sense
        but this is a harder case we will solve later. For the harder case
        this clause then turns into use of all partitions and thus we
        simply set res= -1 as if the mapper had returned that.
        TODO: What to do here is defined in WL#4065.
      */
      if (ppar->arg_stack[0]->part == 0 || ppar->part_info->part_type == VERSIONING_PARTITION)
      {
        uint32 i;
        uint32 store_length_array[MAX_KEY];
        uint32 num_keys= ppar->part_fields;

        for (i= 0; i < num_keys; i++)
          store_length_array[i]= ppar->key[i].store_length;
        res= ppar->part_info->
             get_part_iter_for_interval(ppar->part_info,
                                        FALSE,
                                        store_length_array,
                                        range_par->min_key,
                                        range_par->max_key,
                                        (uint)(tmp_min_key - range_par->min_key),
                                        (uint)(tmp_max_key - range_par->max_key),
                                        flag,
                                        &ppar->part_iter);
        if (!res)
          goto pop_and_go_right; /* res==0 --> no satisfying partitions */
      }
      else
        res= -1;

      if (res == -1)
      {
        /* get a full range iterator */
        init_all_partitions_iterator(ppar->part_info, &ppar->part_iter);
      }
      /* 
        Save our intent to mark full partition as used if we will not be able
        to obtain further limits on subpartitions
      */
      if (key_tree_part < ppar->last_part_partno)
      {
        /*
          We need to ignore the rest of the partitioning fields in all
          evaluations after this
        */
        did_set_ignore_part_fields= TRUE;
        ppar->ignore_part_fields= TRUE;
      }
      set_full_part_if_bad_ret= TRUE;
      goto process_next_key_part;
    }

    if (key_tree_part == ppar->last_subpart_partno && 
        (NULL != ppar->part_info->get_subpart_iter_for_interval))
    {
      PARTITION_ITERATOR subpart_iter;
      DBUG_EXECUTE("info", dbug_print_segment_range(key_tree,
                                                    range_par->key_parts););
      res= ppar->part_info->
           get_subpart_iter_for_interval(ppar->part_info,
                                         TRUE,
                                         NULL, /* Currently not used here */
                                         key_tree->min_value, 
                                         key_tree->max_value,
                                         0, 0, /* Those are ignored here */
                                         key_tree->min_flag |
                                           key_tree->max_flag,
                                         &subpart_iter);
      if (res == 0)
      {
        /*
           The only case where we can get "no satisfying subpartitions"
           returned from the above call is when an error has occurred.
        */
        DBUG_ASSERT(range_par->thd->is_error());
        return 0;
      }

      if (res == -1)
        goto pop_and_go_right; /* all subpartitions satisfy */

      uint32 subpart_id;
      bitmap_clear_all(&ppar->subparts_bitmap);
      while ((subpart_id= subpart_iter.get_next(&subpart_iter)) !=
             NOT_A_PARTITION_ID)
        bitmap_set_bit(&ppar->subparts_bitmap, subpart_id);

      /* Mark each partition as used in each subpartition.  */
      uint32 part_id;
      while ((part_id= ppar->part_iter.get_next(&ppar->part_iter)) !=
              NOT_A_PARTITION_ID)
      {
        for (uint i= 0; i < ppar->part_info->num_subparts; i++)
          if (bitmap_is_set(&ppar->subparts_bitmap, i))
            bitmap_set_bit(&ppar->part_info->read_partitions,
                           part_id * ppar->part_info->num_subparts + i);
      }
      goto pop_and_go_right;
    }

    if (key_tree->is_singlepoint())
    {
      if (key_tree_part == ppar->last_part_partno &&
          ppar->cur_part_fields == ppar->part_fields &&
          ppar->part_info->get_part_iter_for_interval == NULL)
      {
        /* 
          Ok, we've got "fieldN<=>constN"-type SEL_ARGs for all partitioning
          fields. Save all constN constants into table record buffer.
        */
        store_selargs_to_rec(ppar, ppar->arg_stack, ppar->part_fields);
        DBUG_EXECUTE("info", dbug_print_singlepoint_range(ppar->arg_stack,
                                                       ppar->part_fields););
        uint32 part_id;
        longlong func_value;
        /* Find in which partition the {const1, ...,constN} tuple goes */
        if (ppar->get_top_partition_id_func(ppar->part_info, &part_id,
                                            &func_value))
        {
          res= 0; /* No satisfying partitions */
          goto pop_and_go_right;
        }
        /* Remember the limit we got - single partition #part_id */
        init_single_partition_iterator(part_id, &ppar->part_iter);
        
        /*
          If there are no subpartitions/we fail to get any limit for them, 
          then we'll mark full partition as used. 
        */
        set_full_part_if_bad_ret= TRUE;
        goto process_next_key_part;
      }

      if (key_tree_part == ppar->last_subpart_partno &&
          ppar->cur_subpart_fields == ppar->subpart_fields)
      {
        /* 
          Ok, we've got "fieldN<=>constN"-type SEL_ARGs for all subpartitioning
          fields. Save all constN constants into table record buffer.
        */
        store_selargs_to_rec(ppar, ppar->arg_stack_end - ppar->subpart_fields,
                             ppar->subpart_fields);
        DBUG_EXECUTE("info", dbug_print_singlepoint_range(ppar->arg_stack_end- 
                                                       ppar->subpart_fields,
                                                       ppar->subpart_fields););
        /* Find the subpartition (it's HASH/KEY so we always have one) */
        partition_info *part_info= ppar->part_info;
        uint32 part_id, subpart_id;
                 
        if (part_info->get_subpartition_id(part_info, &subpart_id))
          return 0;

        /* Mark this partition as used in each subpartition. */
        while ((part_id= ppar->part_iter.get_next(&ppar->part_iter)) !=
                NOT_A_PARTITION_ID)
        {
          bitmap_set_bit(&part_info->read_partitions,
                         part_id * part_info->num_subparts + subpart_id);
        }
        res= 1; /* Some partitions were marked as used */
        goto pop_and_go_right;
      }
    }
    else
    {
      /* 
        Can't handle condition on current key part. If we're that deep that 
        we're processing subpartitioning's key parts, this means we'll not be
        able to infer any suitable condition, so bail out.
      */
      if (key_tree_part >= ppar->last_part_partno)
      {
        res= -1;
        goto pop_and_go_right;
      }
      /*
        No meaning in continuing with rest of partitioning key parts.
        Will try to continue with subpartitioning key parts.
      */
      ppar->ignore_part_fields= true;
      did_set_ignore_part_fields= true;
      goto process_next_key_part;
    }
  }

process_next_key_part:
  if (key_tree->next_key_part)
    res= find_used_partitions(ppar, key_tree->next_key_part);
  else
    res= -1;

  if (did_set_ignore_part_fields)
  {
    /*
      We have returned from processing all key trees linked to our next
      key part. We are ready to be moving down (using right pointers) and
      this tree is a new evaluation requiring its own decision on whether
      to ignore partitioning fields.
    */
    ppar->ignore_part_fields= FALSE;
  }
  if (set_full_part_if_bad_ret)
  {
    if (res == -1)
    {
      /* Got "full range" for subpartitioning fields */
      uint32 part_id;
      bool found= FALSE;
      while ((part_id= ppar->part_iter.get_next(&ppar->part_iter)) !=
             NOT_A_PARTITION_ID)
      {
        ppar->mark_full_partition_used(ppar->part_info, part_id);
        found= TRUE;
      }
      res= MY_TEST(found);
    }
    /*
      Restore the "used partitions iterator" to the default setting that
      specifies iteration over all partitions.
    */
    init_all_partitions_iterator(ppar->part_info, &ppar->part_iter);
  }

pop_and_go_right:
  /* Pop this key part info off the "stack" */
  ppar->arg_stack_end--;
  ppar->cur_part_fields-=    ppar->is_part_keypart[key_tree_part];
  ppar->cur_subpart_fields-= ppar->is_subpart_keypart[key_tree_part];

  if (res == -1)
    return -1;
  if (key_tree->right != &null_element)
  {
    if (-1 == (right_res= find_used_partitions(ppar,key_tree->right)))
      return -1;
  }
  return (left_res || right_res || res);
}
 

static void mark_all_partitions_as_used(partition_info *part_info)
{
  bitmap_copy(&(part_info->read_partitions),
              &(part_info->lock_partitions));
}


/*
  Check if field types allow to construct partitioning index description
 
  SYNOPSIS
    fields_ok_for_partition_index()
      pfield  NULL-terminated array of pointers to fields.

  DESCRIPTION
    For an array of fields, check if we can use all of the fields to create
    partitioning index description.
    
    We can't process GEOMETRY fields - for these fields singlepoint intervals
    cant be generated, and non-singlepoint are "special" kinds of intervals
    to which our processing logic can't be applied.

    It is not known if we could process ENUM fields, so they are disabled to be
    on the safe side.

  RETURN 
    TRUE   Yes, fields can be used in partitioning index
    FALSE  Otherwise
*/

static bool fields_ok_for_partition_index(Field **pfield)
{
  if (!pfield)
    return FALSE;
  for (; (*pfield); pfield++)
  {
    enum_field_types ftype= (*pfield)->real_type();
    if (ftype == MYSQL_TYPE_ENUM || ftype == MYSQL_TYPE_GEOMETRY)
      return FALSE;
  }
  return TRUE;
}


/*
  Create partition index description and fill related info in the context
  struct

  SYNOPSIS
    create_partition_index_description()
      prune_par  INOUT Partition pruning context

  DESCRIPTION
    Create partition index description. Partition index description is:

      part_index(used_fields_list(part_expr), used_fields_list(subpart_expr))

    If partitioning/sub-partitioning uses BLOB or Geometry fields, then
    corresponding fields_list(...) is not included into index description
    and we don't perform partition pruning for partitions/subpartitions.

  RETURN
    TRUE   Out of memory or can't do partition pruning at all
    FALSE  OK
*/

static bool create_partition_index_description(PART_PRUNE_PARAM *ppar)
{
  RANGE_OPT_PARAM *range_par= &(ppar->range_param);
  partition_info *part_info= ppar->part_info;
  uint used_part_fields, used_subpart_fields;

  used_part_fields= fields_ok_for_partition_index(part_info->part_field_array) ?
                      part_info->num_part_fields : 0;
  used_subpart_fields= 
    fields_ok_for_partition_index(part_info->subpart_field_array)? 
      part_info->num_subpart_fields : 0;
  
  uint total_parts= used_part_fields + used_subpart_fields;

  ppar->ignore_part_fields= FALSE;
  ppar->part_fields=      used_part_fields;
  ppar->last_part_partno= (int)used_part_fields - 1;

  ppar->subpart_fields= used_subpart_fields;
  ppar->last_subpart_partno= 
    used_subpart_fields?(int)(used_part_fields + used_subpart_fields - 1): -1;

  if (part_info->is_sub_partitioned())
  {
    ppar->mark_full_partition_used=  mark_full_partition_used_with_parts;
    ppar->get_top_partition_id_func= part_info->get_part_partition_id;
  }
  else
  {
    ppar->mark_full_partition_used=  mark_full_partition_used_no_parts;
    ppar->get_top_partition_id_func= part_info->get_partition_id;
  }

  KEY_PART *key_part;
  MEM_ROOT *alloc= range_par->mem_root;
  if (!total_parts || 
      !(key_part= (KEY_PART*)alloc_root(alloc, sizeof(KEY_PART)*
                                               total_parts)) ||
      !(ppar->arg_stack= (SEL_ARG**)alloc_root(alloc, sizeof(SEL_ARG*)* 
                                                      total_parts)) ||
      !(ppar->is_part_keypart= (my_bool*)alloc_root(alloc, sizeof(my_bool)*
                                                           total_parts)) ||
      !(ppar->is_subpart_keypart= (my_bool*)alloc_root(alloc, sizeof(my_bool)*
                                                           total_parts)))
    return TRUE;
 
  if (ppar->subpart_fields)
  {
    my_bitmap_map *buf;
    uint32 bufsize= bitmap_buffer_size(ppar->part_info->num_subparts);
    if (!(buf= (my_bitmap_map*) alloc_root(alloc, bufsize)))
      return TRUE;
    my_bitmap_init(&ppar->subparts_bitmap, buf, ppar->part_info->num_subparts);
  }
  range_par->key_parts= key_part;
  Field **field= (ppar->part_fields)? part_info->part_field_array :
                                           part_info->subpart_field_array;
  bool in_subpart_fields= FALSE;
  uint total_key_len= 0;
  for (uint part= 0; part < total_parts; part++, key_part++)
  {
    key_part->key=          0;
    key_part->part=	    part;
    key_part->length= (uint16)(*field)->key_length();
    key_part->store_length= (uint16)get_partition_field_store_length(*field);
    total_key_len += key_part->store_length;

    DBUG_PRINT("info", ("part %u length %u store_length %u", part,
                         key_part->length, key_part->store_length));

    key_part->field=        (*field);
    key_part->image_type =  Field::itRAW;
    /* 
      We set keypart flag to 0 here as the only HA_PART_KEY_SEG is checked
      in the RangeAnalysisModule.
    */
    key_part->flag=         0;
    /* We don't set key_parts->null_bit as it will not be used */

    ppar->is_part_keypart[part]= !in_subpart_fields;
    ppar->is_subpart_keypart[part]= in_subpart_fields;

    /*
      Check if this was last field in this array, in this case we
      switch to subpartitioning fields. (This will only happens if
      there are subpartitioning fields to cater for).
    */
    if (!*(++field))
    {
      field= part_info->subpart_field_array;
      in_subpart_fields= TRUE;
    }
  }
  range_par->key_parts_end= key_part;

  total_key_len++; /* Take into account the "+1" in QUICK_RANGE::QUICK_RANGE */
  if (!(range_par->min_key= (uchar*)alloc_root(alloc,total_key_len)) ||
      !(range_par->max_key= (uchar*)alloc_root(alloc,total_key_len)))
  {
    return true;
  }

  DBUG_EXECUTE("info", print_partitioning_index(range_par->key_parts,
                                                range_par->key_parts_end););
  return FALSE;
}


#ifndef DBUG_OFF

static void print_partitioning_index(KEY_PART *parts, KEY_PART *parts_end)
{
  DBUG_ENTER("print_partitioning_index");
  DBUG_LOCK_FILE;
  fprintf(DBUG_FILE, "partitioning INDEX(");
  for (KEY_PART *p=parts; p != parts_end; p++)
  {
    fprintf(DBUG_FILE, "%s%s", p==parts?"":" ,", p->field->field_name.str);
  }
  fputs(");\n", DBUG_FILE);
  DBUG_UNLOCK_FILE;
  DBUG_VOID_RETURN;
}

/* Print field value into debug trace, in NULL-aware way. */
static void dbug_print_field(Field *field)
{
  if (field->is_real_null())
    fprintf(DBUG_FILE, "NULL");
  else
  {
    char buf[256];
    String str(buf, sizeof(buf), &my_charset_bin);
    str.length(0);
    String *pstr;
    pstr= field->val_str(&str);
    fprintf(DBUG_FILE, "'%s'", pstr->c_ptr_safe());
  }
}


/* Print a "c1 < keypartX < c2" - type interval into debug trace. */
static void dbug_print_segment_range(SEL_ARG *arg, KEY_PART *part)
{
  DBUG_ENTER("dbug_print_segment_range");
  DBUG_LOCK_FILE;
  if (!(arg->min_flag & NO_MIN_RANGE))
  {
    store_key_image_to_rec(part->field, arg->min_value, part->length);
    dbug_print_field(part->field);
    if (arg->min_flag & NEAR_MIN)
      fputs(" < ", DBUG_FILE);
    else
      fputs(" <= ", DBUG_FILE);
  }

  fprintf(DBUG_FILE, "%s", part->field->field_name.str);

  if (!(arg->max_flag & NO_MAX_RANGE))
  {
    if (arg->max_flag & NEAR_MAX)
      fputs(" < ", DBUG_FILE);
    else
      fputs(" <= ", DBUG_FILE);
    store_key_image_to_rec(part->field, arg->max_value, part->length);
    dbug_print_field(part->field);
  }
  fputs("\n", DBUG_FILE);
  DBUG_UNLOCK_FILE;
  DBUG_VOID_RETURN;
}


/*
  Print a singlepoint multi-keypart range interval to debug trace
 
  SYNOPSIS
    dbug_print_singlepoint_range()
      start  Array of SEL_ARG* ptrs representing conditions on key parts
      num    Number of elements in the array.

  DESCRIPTION
    This function prints a "keypartN=constN AND ... AND keypartK=constK"-type 
    interval to debug trace.
*/

static void dbug_print_singlepoint_range(SEL_ARG **start, uint num)
{
  DBUG_ENTER("dbug_print_singlepoint_range");
  DBUG_LOCK_FILE;
  SEL_ARG **end= start + num;

  for (SEL_ARG **arg= start; arg != end; arg++)
  {
    Field *field= (*arg)->field;
    fprintf(DBUG_FILE, "%s%s=", (arg==start)?"":", ", field->field_name.str);
    dbug_print_field(field);
  }
  fputs("\n", DBUG_FILE);
  DBUG_UNLOCK_FILE;
  DBUG_VOID_RETURN;
}
#endif

/****************************************************************************
 * Partition pruning code ends
 ****************************************************************************/
#endif


/*
  Get cost of 'sweep' full records retrieval.
  SYNOPSIS
    get_sweep_read_cost()
      param                 Parameter from test_quick_select
      records               # of records to be retrieved
      add_time_for_compare  If set, add cost of WHERE clause (WHERE_COST)
  RETURN
    cost of sweep
*/

static double get_sweep_read_cost(const PARAM *param, double records,
                                  bool add_time_for_compare)
{
  DBUG_ENTER("get_sweep_read_cost");
#ifndef OLD_SWEEP_COST
  handler *file= param->table->file;
  IO_AND_CPU_COST engine_cost= file->ha_rnd_pos_call_time(double2rows(ceil(records)));
  double cost;
  if (add_time_for_compare)
  {
    engine_cost.cpu+= records * param->thd->variables.optimizer_where_cost;
  }
  cost= file->cost(engine_cost);

  DBUG_PRINT("return", ("cost: %g", cost));
  DBUG_RETURN(cost);
#else
  double result;
  uint pk= param->table->s->primary_key;

  if (param->table->file->pk_is_clustering_key(pk) ||
      param->table->file->stats.block_size == 0 /* HEAP */)
  {
    /*
      We are using the primary key to find the rows.
      Calculate the cost for this.
    */
    result= table->file->ha_rnd_pos_call_time(records);
  }
  else
  {
    /*
      Rows will be retreived with rnd_pos(). Calculate the expected
      cost for this.
    */
    double n_blocks=
      ceil(ulonglong2double(param->table->file->stats.data_file_length) /
           IO_SIZE);
    double busy_blocks=
      n_blocks * (1.0 - pow(1.0 - 1.0/n_blocks, rows2double(records)));
    if (busy_blocks < 1.0)
      busy_blocks= 1.0;
    DBUG_PRINT("info",("sweep: nblocks: %g, busy_blocks: %g", n_blocks,
                       busy_blocks));
    /*
      Disabled: Bail out if # of blocks to read is bigger than # of blocks in
      table data file.
    if (max_cost != DBL_MAX  && (busy_blocks+index_reads_cost) >= n_blocks)
      return 1;
    */
    JOIN *join= param->thd->lex->first_select_lex()->join;
    if (!join || join->table_count == 1)
    {
      /* No join, assume reading is done in one 'sweep' */
      result= busy_blocks*(DISK_SEEK_BASE_COST +
                          DISK_SEEK_PROP_COST*n_blocks/busy_blocks);
    }
    else
    {
      /*
        Possibly this is a join with source table being non-last table, so
        assume that disk seeks are random here.
      */
      result= busy_blocks;
    }
    result+= rows2double(n_rows) * param->table->file->ROW_COPY_COST);
  }
  DBUG_PRINT("return",("cost: %g", result));
  DBUG_RETURN(result);
#endif /* OLD_SWEEP_COST */
}


/*
  Get best plan for a SEL_IMERGE disjunctive expression.
  SYNOPSIS
    get_best_disjunct_quick()
      param     Parameter from check_quick_select function
      imerge    Expression to use
      read_time Don't create scans with cost > read_time

  NOTES
    index_merge cost is calculated as follows:
    index_merge_cost =
      cost(index_reads) +         (see #1)
      cost(rowid_to_row_scan) +   (see #2)
      cost(unique_use)            (see #3)

    1. cost(index_reads) =SUM_i(cost(index_read_i))
       For non-CPK scans,
         cost(index_read_i) = {cost of ordinary 'index only' scan}
       For CPK scan,
         cost(index_read_i) = {cost of non-'index only' scan}

    2. cost(rowid_to_row_scan)
      If table PK is clustered then
        cost(rowid_to_row_scan) =
          {cost of ordinary clustered PK scan with n_ranges=n_rows}

      Otherwise, we use the following model to calculate costs:
      We need to retrieve n_rows rows from file that occupies n_blocks blocks.
      We assume that offsets of rows we need are independent variates with
      uniform distribution in [0..max_file_offset] range.

      We'll denote block as "busy" if it contains row(s) we need to retrieve
      and "empty" if doesn't contain rows we need.

      Probability that a block is empty is (1 - 1/n_blocks)^n_rows (this
      applies to any block in file). Let x_i be a variate taking value 1 if
      block #i is empty and 0 otherwise.

      Then E(x_i) = (1 - 1/n_blocks)^n_rows;

      E(n_empty_blocks) = E(sum(x_i)) = sum(E(x_i)) =
        = n_blocks * ((1 - 1/n_blocks)^n_rows) =
       ~= n_blocks * exp(-n_rows/n_blocks).

      E(n_busy_blocks) = n_blocks*(1 - (1 - 1/n_blocks)^n_rows) =
       ~= n_blocks * (1 - exp(-n_rows/n_blocks)).

      Average size of "hole" between neighbor non-empty blocks is
           E(hole_size) = n_blocks/E(n_busy_blocks).

      The total cost of reading all needed blocks in one "sweep" is:

      E(n_busy_blocks)*
       (DISK_SEEK_BASE_COST + DISK_SEEK_PROP_COST*n_blocks/E(n_busy_blocks)).

    3. Cost of Unique use is calculated in Unique::get_use_cost function.

  ROR-union cost is calculated in the same way index_merge, but instead of
  Unique a priority queue is used.

  RETURN
    Created read plan
    NULL - Out of memory or no read scan could be built.
*/

static
TABLE_READ_PLAN *get_best_disjunct_quick(PARAM *param,
                                         bool index_merge_union_allowed,
                                         bool index_merge_sort_union_allowed,
                                         SEL_IMERGE *imerge,
                                         double read_time,
                                         ha_rows limit,
                                         bool named_trace,
                                         bool using_table_scan)
{
  SEL_TREE **ptree;
  TRP_INDEX_MERGE *imerge_trp= NULL;
  TRP_RANGE **range_scans;
  TRP_RANGE **cur_child;
  TRP_RANGE **cpk_scan= NULL;
  bool imerge_too_expensive= FALSE;
  double imerge_cost= 0.0;
  ha_rows cpk_scan_records= 0;
  ha_rows non_cpk_scan_records= 0;
  bool all_scans_ror_able= TRUE;
  bool all_scans_rors= TRUE;
  uint unique_calc_buff_size;
  TABLE_READ_PLAN **roru_read_plans;
  TABLE_READ_PLAN **cur_roru_plan;
  double roru_index_costs;
  ha_rows roru_total_records;
  double roru_intersect_part= 1.0;
  size_t n_child_scans;
  double limit_read_time= read_time;
  THD *thd= param->thd;
  DBUG_ENTER("get_best_disjunct_quick");
  DBUG_PRINT("info", ("Full table scan cost: %g", read_time));

  /*
    In every tree of imerge remove SEL_ARG trees that do not make ranges.
    If after this removal some SEL_ARG tree becomes empty discard imerge.
  */
  for (ptree= imerge->trees; ptree != imerge->trees_next; ptree++)
  {
    if (remove_nonrange_trees(param, *ptree))
    {
      imerge->trees_next= imerge->trees;
      break;
    }
  }

  const bool force_index_merge =
      hint_table_state(thd, param->table, INDEX_MERGE_HINT_ENUM, 0);

  n_child_scans= imerge->trees_next - imerge->trees;

  if (!n_child_scans)
    DBUG_RETURN(NULL);

  if (!(range_scans= (TRP_RANGE**)alloc_root(param->mem_root,
                                             sizeof(TRP_RANGE*)*
                                             n_child_scans)))
    DBUG_RETURN(NULL);

  const char* trace_best_disjunct_obj_name= named_trace ? "best_disjunct_quick" : nullptr;
  Json_writer_object trace_best_disjunct(thd, trace_best_disjunct_obj_name);
  Json_writer_array to_merge(thd, "indexes_to_merge");
  /*
    Collect best 'range' scan for each of disjuncts, and, while doing so,
    analyze possibility of ROR scans. Also calculate some values needed by
    other parts of the code.
  */
  for (ptree= imerge->trees, cur_child= range_scans;
       ptree != imerge->trees_next;
       ptree++, cur_child++)
  {
    DBUG_EXECUTE("info", print_sel_tree(param, *ptree, &(*ptree)->keys_map,
                                        "tree in SEL_IMERGE"););
    Json_writer_object trace_idx(thd);
    if (!(*cur_child= get_key_scans_params(param, *ptree, TRUE, FALSE,
                                           read_time, limit, using_table_scan)))
    {
      /*
        One of index scans in this index_merge is more expensive than entire
        table read for another available option. The entire index_merge (and
        any possible ROR-union) will be more expensive then, too. We continue
        here only to update SQL_SELECT members.
      */
      imerge_too_expensive= TRUE;
    }
    if (imerge_too_expensive)
    {
      trace_idx.add("chosen", false).add("cause", "cost");
      continue;
    }
    const uint keynr_in_table= param->real_keynr[(*cur_child)->key_idx];
    imerge_cost += (*cur_child)->read_cost;
    all_scans_ror_able &= ((*ptree)->n_ror_scans > 0);
    all_scans_rors &= (*cur_child)->is_ror;
    if (param->table->file->is_clustering_key(keynr_in_table))
    {
      cpk_scan= cur_child;
      cpk_scan_records= (*cur_child)->records;
    }
    else
      non_cpk_scan_records += (*cur_child)->records;
    if (unlikely(trace_idx.trace_started()))
      trace_idx.
        add("index_to_merge", param->table->key_info[keynr_in_table].name).
        add("cumulated_cost", imerge_cost);
  }

  to_merge.end();

  DBUG_PRINT("info", ("index_merge scans cost %g", imerge_cost));
  trace_best_disjunct.add("cost_of_reading_ranges", imerge_cost);

  if (imerge_too_expensive || (((imerge_cost > read_time) ||
                               ((non_cpk_scan_records+cpk_scan_records >=
                                 param->table->stat_records()) &&
                                read_time != DBL_MAX)) &&
                               !force_index_merge))
  {
    /*
      Bail out if it is obvious that both index_merge and ROR-union will be
      more expensive
    */
    DBUG_PRINT("info", ("Sum of index_merge scans is more expensive than "
                        "full table scan, bailing out"));
    trace_best_disjunct.add("chosen", false).add("cause", "cost");
    DBUG_RETURN(NULL);
  }

  /*
    If all scans happen to be ROR, proceed to generate a ROR-union plan (it's
    guaranteed to be cheaper than non-ROR union), unless ROR-unions are
    disabled in @@optimizer_switch
  */
  if (all_scans_rors && (index_merge_union_allowed || force_index_merge))
  {
    roru_read_plans= (TABLE_READ_PLAN**)range_scans;
    if (unlikely(trace_best_disjunct.trace_started()))
      trace_best_disjunct.
        add("use_roworder_union", true).
        add("cause", "always cheaper than non roworder retrieval");
    goto skip_to_ror_scan;
  }

  if (cpk_scan)
  {
    /*
      Add one ROWID comparison for each row retrieved on non-CPK scan.  (it
      is done in QUICK_RANGE_SELECT::row_in_ranges)
     */
    double rid_comp_cost= (rows2double(non_cpk_scan_records) *
                           default_optimizer_costs.rowid_cmp_cost);
    imerge_cost+= rid_comp_cost;
    trace_best_disjunct.add("cost_of_mapping_rowid_in_non_clustered_pk_scan",
                            rid_comp_cost);
  }

  /* Calculate cost(rowid_to_row_scan) */
  {
    /* imerge_cost already includes WHERE_COST */
    double sweep_cost= get_sweep_read_cost(param, rows2double(non_cpk_scan_records), 0);
    imerge_cost+= sweep_cost;
    trace_best_disjunct.
      add("rows", non_cpk_scan_records).
      add("cost_sort_rowid_and_read_disk", sweep_cost).
      add("cost", imerge_cost);
  }
  DBUG_PRINT("info",("index_merge cost with rowid-to-row scan: %g",
                     imerge_cost));
  if ((imerge_cost > read_time || !index_merge_sort_union_allowed) &&
      !force_index_merge)
  {
    if (unlikely(trace_best_disjunct.trace_started()))
      trace_best_disjunct.
        add("use_sort_index_merge", false).
        add("cause", imerge_cost > read_time ? "cost" : "disabled");
    goto build_ror_index_merge;                 // Try roworder_index_merge
  }

  /* Add Unique operations cost */
  unique_calc_buff_size=
    Unique::get_cost_calc_buff_size((ulong)non_cpk_scan_records,
                                    param->table->file->ref_length,
                                    (size_t)param->thd->variables.sortbuff_size);
  if (param->imerge_cost_buff_size < unique_calc_buff_size)
  {
    if (!(param->imerge_cost_buff= (uint*)alloc_root(param->mem_root,
                                                     unique_calc_buff_size)))
      DBUG_RETURN(NULL);
    param->imerge_cost_buff_size= unique_calc_buff_size;
  }

  {
    const double dup_removal_cost= Unique::get_use_cost(thd,
                           param->imerge_cost_buff, (uint)non_cpk_scan_records,
                           param->table->file->ref_length,
                           (size_t)param->thd->variables.sortbuff_size,
                           ROWID_COMPARE_COST_THD(param->thd),
                           FALSE, NULL);
    imerge_cost+= dup_removal_cost;
    if (unlikely(trace_best_disjunct.trace_started()))
      trace_best_disjunct.
        add("cost_duplicate_removal", dup_removal_cost).
        add("total_cost", imerge_cost);
  }

  DBUG_PRINT("info",("index_merge total cost: %g (wanted: less then %g)",
                     imerge_cost, read_time));
  if (imerge_cost < read_time || force_index_merge)
  {
    if ((imerge_trp= new (param->mem_root)TRP_INDEX_MERGE))
    {
      imerge_trp->force_index_merge= force_index_merge;
      imerge_trp->read_cost= imerge_cost;
      imerge_trp->records= non_cpk_scan_records + cpk_scan_records;
      imerge_trp->records= MY_MIN(imerge_trp->records,
                               param->table->stat_records());
      imerge_trp->range_scans= range_scans;
      imerge_trp->range_scans_end= range_scans + n_child_scans;
      read_time= imerge_cost;
    }
    if (imerge_trp)
    {
      TABLE_READ_PLAN *trp= merge_same_index_scans(param, imerge, imerge_trp,
                                                   limit_read_time,
                                                   index_merge_union_allowed,
                                                   index_merge_sort_union_allowed);
      if (trp != imerge_trp)
        DBUG_RETURN(trp);
    }
  }

build_ror_index_merge:
  if (!all_scans_ror_able || param->thd->lex->sql_command == SQLCOM_DELETE ||
      (!index_merge_union_allowed && !force_index_merge))
    DBUG_RETURN(imerge_trp);

  /* Ok, it is possible to build a ROR-union, try it. */
  bool dummy;
  if (!(roru_read_plans=
          (TABLE_READ_PLAN**)alloc_root(param->mem_root,
                                        sizeof(TABLE_READ_PLAN*)*
                                        n_child_scans)))
    DBUG_RETURN(imerge_trp);

skip_to_ror_scan:
  roru_index_costs= 0.0;
  roru_total_records= 0;
  cur_roru_plan= roru_read_plans;

  Json_writer_array trace_analyze_ror(thd, "analyzing_roworder_scans");

  /* Find 'best' ROR scan for each of trees in disjunction */
  for (ptree= imerge->trees, cur_child= range_scans;
       ptree != imerge->trees_next;
       ptree++, cur_child++, cur_roru_plan++)
  {
    Json_writer_object trp_info(thd);
    if (unlikely(thd->trace_started()))
      (*cur_child)->trace_basic_info(param, &trp_info);
    /*
      Assume the best ROR scan is the one that has cheapest full-row-retrieval
      scan cost.
      Also accumulate index_only scan costs as we'll need them to calculate
      overall index_intersection cost.
    */
    double cost;
    if ((*cur_child)->is_ror)
    {
      handler *file= param->table->file;
      /* Ok, we have index_only cost, now get full rows scan cost */
      cost= file->cost(file->ha_rnd_pos_call_and_compare_time((*cur_child)->records));
    }
    else
      cost= read_time;

    TABLE_READ_PLAN *prev_plan= *cur_child;
    TRP_ROR_INTERSECT *ror_trp;
    if (!(*cur_roru_plan= ror_trp= get_best_ror_intersect(param, *ptree, cost,
                                                          &dummy, false)))
    {
      if (!prev_plan->is_ror)
        DBUG_RETURN(imerge_trp);
      *cur_roru_plan= prev_plan;
      roru_index_costs += (*cur_roru_plan)->read_cost;
    }
    else
      roru_index_costs += ror_trp->index_scan_costs;
    roru_total_records += (*cur_roru_plan)->records;
    roru_intersect_part *= ((*cur_roru_plan)->records /
                            param->table->stat_records());
  }
  trace_analyze_ror.end();
  /*
    rows to retrieve=
      SUM(rows_in_scan_i) - table_rows * PROD(rows_in_scan_i / table_rows).
    This is valid because index_merge construction guarantees that conditions
    in disjunction do not share key parts.
  */
  roru_total_records -= (ha_rows)(roru_intersect_part*
                                  param->table->stat_records());
  /* ok, got a ROR read plan for each of the disjuncts
    Calculate cost:
    cost(index_union_scan(scan_1, ... scan_n)) =
      SUM_i(cost_of_index_only_scan(scan_i)) +
      queue_use_cost(rowid_len, n) +
      cost_of_row_retrieval
    See get_merge_buffers_cost function for queue_use_cost formula derivation.
  */

  double roru_total_cost;
  roru_total_cost= (roru_index_costs +
                    rows2double(roru_total_records)*log((double)n_child_scans) *
                    ROWID_COMPARE_COST_THD(param->thd) / M_LN2 +
                    get_sweep_read_cost(param, rows2double(roru_total_records), 0));

  DBUG_PRINT("info", ("ROR-union: cost %g, %zu members",
                      roru_total_cost, n_child_scans));
  if (unlikely(trace_best_disjunct.trace_started()))
    trace_best_disjunct.
      add("index_roworder_union_cost", roru_total_cost).
      add("members", n_child_scans);
  TRP_ROR_UNION* roru;
  if (roru_total_cost < read_time || force_index_merge)
  {
    if ((roru= new (param->mem_root) TRP_ROR_UNION))
    {
      trace_best_disjunct.add("chosen", true);
      roru->force_index_merge= force_index_merge;
      roru->first_ror= roru_read_plans;
      roru->last_ror= roru_read_plans + n_child_scans;
      roru->read_cost= roru_total_cost;
      roru->records= roru_total_records;
      DBUG_RETURN(roru);
    }
  }
  else
    trace_best_disjunct.add("chosen", false);
  DBUG_RETURN(imerge_trp);
}


/*
  Merge index scans for the same indexes in an index merge plan

  SYNOPSIS
    merge_same_index_scans()
      param           Context info for the operation
      imerge   IN/OUT SEL_IMERGE from which imerge_trp has been extracted
      imerge_trp      The index merge plan where index scans for the same
                      indexes are to be merges
      read_time       The upper bound for the cost of the plan to be evaluated

  DESCRIPTION
    For the given index merge plan imerge_trp extracted from the SEL_MERGE
    imerge the function looks for range scans with the same indexes and merges
    them into SEL_ARG trees. Then for each such SEL_ARG tree r_i the function
    creates a range tree rt_i that contains only r_i. All rt_i are joined
    into one index merge that replaces the original index merge imerge.
    The function calls get_best_disjunct_quick for the new index merge to
    get a new index merge plan that contains index scans only for different
    indexes.
    If there are no index scans for the same index in the original index
    merge plan the function does not change the original imerge and returns
    imerge_trp as its result.

  RETURN
    The original or or improved index merge plan                        
*/

static
TABLE_READ_PLAN *merge_same_index_scans(PARAM *param, SEL_IMERGE *imerge,
                                        TRP_INDEX_MERGE *imerge_trp,
                                        double read_time,
                                        bool index_merge_union_allowed,
                                        bool index_merge_sort_union_allowed)
{
  uint16 first_scan_tree_idx[MAX_KEY];
  SEL_TREE **tree;
  TRP_RANGE **cur_child;
  uint removed_cnt= 0;

  DBUG_ENTER("merge_same_index_scans");

  bzero(first_scan_tree_idx, sizeof(first_scan_tree_idx[0])*param->keys);

  for (tree= imerge->trees, cur_child= imerge_trp->range_scans;
       tree != imerge->trees_next;
       tree++, cur_child++)
  {
    DBUG_ASSERT(tree);
    uint key_idx= (*cur_child)->key_idx;
    uint16 *tree_idx_ptr= &first_scan_tree_idx[key_idx];
    if (!*tree_idx_ptr)
      *tree_idx_ptr= (uint16) (tree-imerge->trees+1);
    else
    {
      SEL_TREE **changed_tree= imerge->trees+(*tree_idx_ptr-1);
      SEL_ARG *key= (*changed_tree)->keys[key_idx];
      for (uint i= 0; i < param->keys; i++)
        (*changed_tree)->keys[i]= NULL;
      (*changed_tree)->keys_map.clear_all();
      if (key) 
        key->incr_refs(); 
      if ((*tree)->keys[key_idx]) 
        (*tree)->keys[key_idx]->incr_refs(); 
      if (((*changed_tree)->keys[key_idx]=
             key_or_with_limit(param, key_idx, key, (*tree)->keys[key_idx])))
        (*changed_tree)->keys_map.set_bit(key_idx);
      *tree= NULL;
      removed_cnt++;
    }
  }
  if (!removed_cnt)
    DBUG_RETURN(imerge_trp);

  TABLE_READ_PLAN *trp= NULL;
  SEL_TREE **new_trees_next= imerge->trees;
  for (tree= new_trees_next; tree != imerge->trees_next; tree++)
  {
    if (!*tree)
      continue;
    if (tree > new_trees_next)
      *new_trees_next= *tree;
    new_trees_next++;
  }
  imerge->trees_next= new_trees_next;

  DBUG_ASSERT(imerge->trees_next>imerge->trees);

  if (imerge->trees_next-imerge->trees > 1)
    trp= get_best_disjunct_quick(param, index_merge_union_allowed, index_merge_sort_union_allowed, imerge, read_time,
                                 HA_POS_ERROR, true, 0);
  else
  {
    /*
      This alternative theoretically can be reached when the cost
      of the index merge for such a formula as
        (key1 BETWEEN c1_1 AND c1_2) AND key2 > c2 OR
        (key1 BETWEEN c1_3 AND c1_4) AND key3 > c3
      is estimated as being cheaper than the cost of index scan for
      the formula
        (key1 BETWEEN c1_1 AND c1_2) OR (key1 BETWEEN c1_3 AND c1_4)
      
      In the current code this may happen for two reasons:
      1. for a single index range scan data records are accessed in
         a random order
      2. the functions that estimate the cost of a range scan and an
         index merge retrievals are not well calibrated

      As the best range access has been already chosen it does not
      make sense to evaluate the one obtained from a degenerated
      index merge.
    */
    trp= 0;
  }

  DBUG_RETURN(trp); 
}


/*
  This structure contains the info common for all steps of a partial
  index intersection plan. Moreover it contains also the info common
  for index intersect plans. This info is filled in by the function
  prepare_search_best just before searching for the best index
  intersection plan.
*/  

typedef struct st_common_index_intersect_info
{
  PARAM *param;           /* context info for range optimizations            */
  uint key_size;          /* size of a ROWID element stored in Unique object */
  double compare_factor;  /* cost to compare two ROWIDs                      */
  size_t max_memory_size;   /* maximum space allowed for Unique objects      */
  ha_rows table_cardinality;   /* estimate of the number of records in table */
  double cutoff_cost;        /* discard index intersects with greater costs  */ 
  INDEX_SCAN_INFO *cpk_scan;  /* clustered primary key used in intersection  */

  bool in_memory;  /* unique object for intersection is completely in memory */

  INDEX_SCAN_INFO **search_scans;    /* scans possibly included in intersect */ 
  uint n_search_scans;               /* number of elements in search_scans   */

  bool best_uses_cpk;   /* current best intersect uses clustered primary key */
  double best_cost;       /* cost of the current best index intersection     */
  /* estimate of the number of records in the current best intersection      */
  ha_rows best_records;
  uint best_length;    /* number of indexes in the current best intersection */
  INDEX_SCAN_INFO **best_intersect;  /* the current best index intersection  */
  /* scans from the best intersect to be filtered by cpk conditions         */
  key_map filtered_scans; 

  uint *buff_elems;        /* buffer to calculate cost of index intersection */
  
} COMMON_INDEX_INTERSECT_INFO;


/*
  This structure contains the info specific for one step of an index
  intersection plan. The structure is filled in by the function 
   check_index_intersect_extension.
*/

typedef struct st_partial_index_intersect_info
{
  COMMON_INDEX_INTERSECT_INFO *common_info;    /* shared by index intersects */
  uint length;         /* number of index scans in the partial intersection  */
  ha_rows records;     /* estimate of the number of records in intersection  */
  double cost;         /* cost of the partial index intersection             */

  /* estimate of total number of records of all scans of the partial index
     intersect sent to the Unique object used for the intersection  */
  ha_rows records_sent_to_unique;

  /* total cost of the scans of indexes from the partial index intersection  */
  double index_read_cost; 

  bool use_cpk_filter;      /* cpk filter is to be used for this       scan  */  
  bool in_memory;            /* uses unique object in memory                 */
  double in_memory_cost;     /* cost of using unique object in memory        */

  key_map filtered_scans;    /* scans to be filtered by cpk conditions       */
         
  MY_BITMAP *intersect_fields;     /* bitmap of fields used in intersection  */

  void init()
  {
    common_info= NULL;
    intersect_fields= NULL;
    records_sent_to_unique= records= length= in_memory= use_cpk_filter= 0;
    cost= index_read_cost= in_memory_cost= 0.0;
    filtered_scans.clear_all();
  }
} PARTIAL_INDEX_INTERSECT_INFO;


/* Check whether two indexes have the same first n components */

static
bool same_index_prefix(KEY *key1, KEY *key2, uint used_parts)
{
  KEY_PART_INFO *part1= key1->key_part;
  KEY_PART_INFO *part2= key2->key_part;
  for(uint i= 0; i < used_parts; i++, part1++, part2++)
  {
    if (part1->fieldnr != part2->fieldnr)
      return FALSE;
  }
  return TRUE;
}


/* Create a bitmap for all fields of a table */

static
bool create_fields_bitmap(PARAM *param, MY_BITMAP *fields_bitmap)
{
  my_bitmap_map *bitmap_buf;

  if (!(bitmap_buf= (my_bitmap_map *) alloc_root(param->mem_root,
                                                 param->fields_bitmap_size)))
    return TRUE;
  if (my_bitmap_init(fields_bitmap, bitmap_buf, param->table->s->fields))
    return TRUE;
  
  return FALSE;
}

/* Compare two indexes scans for sort before search for the best intersection */

static
int cmp_intersect_index_scan(const void *a_, const void *b_)
{
  auto a= static_cast<const INDEX_SCAN_INFO *const *>(a_);
  auto b= static_cast<const INDEX_SCAN_INFO *const *>(b_);
  return CMP_NUM((*a)->records, (*b)->records);
}


static inline
void set_field_bitmap_for_index_prefix(MY_BITMAP *field_bitmap,
                                       KEY_PART_INFO *key_part,
                                       uint used_key_parts)
{
  bitmap_clear_all(field_bitmap);
  for (KEY_PART_INFO *key_part_end= key_part+used_key_parts;
       key_part < key_part_end; key_part++)
  {
    bitmap_set_bit(field_bitmap, key_part->fieldnr-1);
  }
}


/*
  Round up table cardinality read from statistics provided by engine.
  This function should go away when mysql test will allow to handle
  more or less easily in the test suites deviations of InnoDB 
  statistical data.
*/
 
static inline
ha_rows get_table_cardinality_for_index_intersect(TABLE *table)
{
  if (table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT)
    return table->stat_records();
  else
  {
    ha_rows d;
    double q;
    for (q= (double)table->stat_records(), d= 1 ; q >= 10; q/= 10, d*= 10 ) ;
    return (ha_rows) (floor(q+0.5) * d);
  } 
}

static
void print_keyparts(THD *thd, KEY *key, uint key_parts)
{
  DBUG_ASSERT(thd->trace_started());

  KEY_PART_INFO *part= key->key_part;
  Json_writer_array keyparts(thd, "keyparts");
  for(uint i= 0; i < key_parts; i++, part++)
    keyparts.add(part->field->field_name);
}

  
static
ha_rows records_in_index_intersect_extension(PARTIAL_INDEX_INTERSECT_INFO *curr,
                                             INDEX_SCAN_INFO *ext_index_scan);

/*
  Prepare to search for the best index intersection

  SYNOPSIS
    prepare_search_best_index_intersect()
      param         common info about index ranges
      tree          tree of ranges for indexes that can be intersected
      common    OUT info needed for search to be filled by the function 
      init      OUT info for an initial pseudo step of the intersection plans
      cutoff_cost   cut off cost of the interesting index intersection 

  DESCRIPTION
    The function initializes all fields of the structure 'common' to be used
    when searching for the best intersection plan. It also allocates
    memory to store the most cheap index intersection.

  NOTES
    When selecting candidates for index intersection we always take only
    one representative out of any set of indexes that share the same range
    conditions. These indexes always have the same prefixes and the
    components of this prefixes are exactly those used in these range
    conditions.
    Range conditions over clustered primary key (cpk) is always used only
    as the condition that filters out some rowids retrieved by the scans
    for secondary indexes. The cpk index will be handled in special way by
    the function that search for the best index intersection. 

  RETURN
    FALSE  in the case of success
    TRUE   otherwise
*/

static
bool prepare_search_best_index_intersect(PARAM *param, 
                                         SEL_TREE *tree,
                                         COMMON_INDEX_INTERSECT_INFO *common,
                                         PARTIAL_INDEX_INTERSECT_INFO *init,
                                         double cutoff_cost)
{
  uint i;
  uint n_search_scans;
  double cost;
  INDEX_SCAN_INFO **index_scan;
  INDEX_SCAN_INFO **scan_ptr;
  INDEX_SCAN_INFO *cpk_scan= NULL;
  TABLE *table= param->table;
  uint n_index_scans= (uint)(tree->index_scans_end - tree->index_scans);
  THD *thd= param->thd;

  if (n_index_scans <= 1)
    return 1;

  init->init();
  init->common_info= common;
  init->cost= cutoff_cost;

  common->param= param;
  common->key_size= table->file->ref_length;
  common->compare_factor= ROWID_COMPARE_COST_THD(param->thd);
  common->max_memory_size= (size_t)param->thd->variables.sortbuff_size;
  common->cutoff_cost= cutoff_cost;
  common->cpk_scan= NULL;
  common->table_cardinality= 
    get_table_cardinality_for_index_intersect(table);

  if (table->file->ha_table_flags() & HA_TABLE_SCAN_ON_INDEX)
  {
    INDEX_SCAN_INFO **index_scan_end;
    index_scan= tree->index_scans;
    index_scan_end= index_scan+n_index_scans;
    for ( ; index_scan < index_scan_end; index_scan++)
    {  
      if (table->file->is_clustering_key((*index_scan)->keynr))
      {
        common->cpk_scan= cpk_scan= *index_scan;
        break;
      }
    }
  }

  i= n_index_scans - MY_TEST(cpk_scan != NULL) + 1;

  if (!(common->search_scans =
	(INDEX_SCAN_INFO **) alloc_root (param->mem_root,
                                         sizeof(INDEX_SCAN_INFO *) * i)))
    return TRUE;
  bzero(common->search_scans, sizeof(INDEX_SCAN_INFO *) * i);

  INDEX_SCAN_INFO **selected_index_scans= common->search_scans;
  Json_writer_array potential_idx_scans(thd, "potential_index_scans");
  for (i=0, index_scan= tree->index_scans; i < n_index_scans; i++, index_scan++)
  {
    Json_writer_object idx_scan(thd);
    uint used_key_parts= (*index_scan)->used_key_parts;
    KEY *key_info= (*index_scan)->key_info;
    idx_scan.add("index", key_info->name);

    if (*index_scan == cpk_scan)
    {
      if (unlikely(idx_scan.trace_started()))
        idx_scan.
          add("chosen", "false").
          add("cause", "clustered index used for filtering");
      continue;
    }
    if (cpk_scan && cpk_scan->used_key_parts >= used_key_parts &&
        same_index_prefix(cpk_scan->key_info, key_info, used_key_parts))
    {
      if (unlikely(idx_scan.trace_started()))
        idx_scan.
          add("chosen", "false").
          add("cause", "clustered index used for filtering");
      continue;
    }

    cost= table->opt_range[(*index_scan)->keynr].index_only_fetch_cost(table);

    idx_scan.add("cost", cost);

    if (cost + COST_EPS >= cutoff_cost)
    {
      if (unlikely(idx_scan.trace_started()))
        idx_scan.add("chosen", false).add("cause", "cost");
      continue;
    }
   
    for (scan_ptr= selected_index_scans; *scan_ptr ; scan_ptr++)
    {
      /*
        When we have range conditions for two different indexes with the same
        beginning it does not make sense to consider both of them for index 
        intersection if the range conditions are covered by common initial
        components of the indexes. Actually in this case the indexes are
        guaranteed to have the same range conditions.
      */
      if ((*scan_ptr)->used_key_parts == used_key_parts &&
          same_index_prefix((*scan_ptr)->key_info, key_info, used_key_parts))
        break;
    }
    if (!*scan_ptr || cost < (*scan_ptr)->index_read_cost)
    {
      if (unlikely(idx_scan.trace_started()))
      {
        idx_scan.add("chosen", true);
        if (!*scan_ptr)
          idx_scan.add("cause", "first occurrence of index prefix");
        else
          idx_scan.add("cause", "better cost for same idx prefix");
      }
      *scan_ptr= *index_scan;
      (*scan_ptr)->index_read_cost= cost;
    }
    else if (unlikely(idx_scan.trace_started()))
    {
      idx_scan.add("chosen", false).add("cause", "cost");
    }
  }
  potential_idx_scans.end();

  ha_rows records_in_scans= 0;

  for (scan_ptr=selected_index_scans, i= 0; *scan_ptr; scan_ptr++, i++)
  {
    if (create_fields_bitmap(param, &(*scan_ptr)->used_fields))
      return TRUE;
    records_in_scans+= (*scan_ptr)->records;
  }

  n_search_scans= i;

  if (cpk_scan && create_fields_bitmap(param, &cpk_scan->used_fields))
    return TRUE;
  
  if (!(common->n_search_scans= n_search_scans))
    return TRUE;
    
  common->best_uses_cpk= FALSE;
  common->best_cost= cutoff_cost;
  common->best_length= 0;

  if (!(common->best_intersect=
	(INDEX_SCAN_INFO **) alloc_root (param->mem_root,
                                         sizeof(INDEX_SCAN_INFO *) *
                                         (i + MY_TEST(cpk_scan != NULL)))))
    return TRUE;

  size_t calc_cost_buff_size=
         Unique::get_cost_calc_buff_size((size_t)records_in_scans,
                                         common->key_size,
				         common->max_memory_size);
  if (!(common->buff_elems= (uint *) alloc_root(param->mem_root,
                                                calc_cost_buff_size)))
    return TRUE;

  my_qsort(selected_index_scans, n_search_scans, sizeof(INDEX_SCAN_INFO *),
           cmp_intersect_index_scan);

  Json_writer_array selected_idx_scans(thd, "selected_index_scans");
  if (cpk_scan)
  {
    PARTIAL_INDEX_INTERSECT_INFO curr;
    set_field_bitmap_for_index_prefix(&cpk_scan->used_fields,
                                      cpk_scan->key_info->key_part,
                                      cpk_scan->used_key_parts);
    curr.common_info= common;
    curr.intersect_fields= &cpk_scan->used_fields;
    curr.records= cpk_scan->records;
    curr.length= 1;
    for (scan_ptr=selected_index_scans; *scan_ptr; scan_ptr++)
    {
      KEY *key_info= (*scan_ptr)->key_info;
      ha_rows scan_records= (*scan_ptr)->records;
      ha_rows records= records_in_index_intersect_extension(&curr, *scan_ptr);
      (*scan_ptr)->filtered_out= records >= scan_records ?
                                   0 : scan_records-records;
      if (unlikely(thd->trace_started()))
      {
        Json_writer_object selected_idx(thd);
        selected_idx.add("index", key_info->name);
        print_keyparts(thd, key_info, (*scan_ptr)->used_key_parts);
        selected_idx.
          add("rows", (*scan_ptr)->records).
          add("filtered_records", (*scan_ptr)->filtered_out);
      }
    }
  } 
  else
  {
    for (scan_ptr=selected_index_scans; *scan_ptr; scan_ptr++)
    {
      KEY *key_info= (*scan_ptr)->key_info;
      (*scan_ptr)->filtered_out= 0;
      if (unlikely(thd->trace_started()))
      {
        Json_writer_object selected_idx(thd);
        selected_idx.add("index", key_info->name);
        print_keyparts(thd, key_info, (*scan_ptr)->used_key_parts);
        selected_idx.
          add("rows", (*scan_ptr)->records).
          add("filtered_records", (*scan_ptr)->filtered_out);
      }
    }
  }

  return FALSE;
}


/*
  On Estimation of the Number of Records in an Index Intersection 
  ===============================================================

  Consider query Q over table t. Let C be the WHERE condition of  this query,
  and, idx1(a1_1,...,a1_k1) and idx2(a2_1,...,a2_k2) be some indexes defined
  on table t.
  Let rt1 and rt2 be the range trees extracted by the range optimizer from C
  for idx1 and idx2 respectively.
  Let #t be the estimate of the number of records in table t provided for the
  optimizer. 
  Let #r1 and #r2 be the estimates of the number of records in the range trees
  rt1 and rt2, respectively, obtained by the range optimizer.

  We need to get an estimate for the number of records in the index 
  intersection of rt1 and rt2. In other words, we need to estimate the
  cardinality of the set of records that are in both trees. Let's designate
  this number by #r.

  If we do not make any assumptions then we can only state that
     #r<=MY_MIN(#r1,#r2).
  With this estimate we can't say that the index intersection scan will be 
  cheaper than the cheapest index scan.

  Let Rt1 and Rt2 be AND/OR conditions representing rt and rt2 respectively.
  The probability that a record belongs to rt1 is sel(Rt1)=#r1/#t.
  The probability that a record belongs to rt2 is sel(Rt2)=#r2/#t.

  If we assume that the values in columns of idx1 and idx2 are independent
  then #r/#t=sel(Rt1&Rt2)=sel(Rt1)*sel(Rt2)=(#r1/#t)*(#r2/#t).
  So in this case we have: #r=#r1*#r2/#t.

  The above assumption of independence of the columns in idx1 and idx2 means
  that:
  - all columns are different
  - values from one column do not correlate with values from any other column.

  We can't help with the case when column correlate with each other.
  Yet, if they are assumed to be uncorrelated the value of #r theoretically can
  be evaluated . Unfortunately this evaluation, in general, is rather complex.

  Let's consider two indexes idx1:(dept, manager),  idx2:(dept, building)
  over table 'employee' and two range conditions over these indexes:
    Rt1: dept=10 AND manager LIKE 'S%'
    Rt2: dept=10 AND building LIKE 'L%'.
  We can state that:
    sel(Rt1&Rt2)=sel(dept=10)*sel(manager LIKE 'S%')*sel(building LIKE 'L%')
    =sel(Rt1)*sel(Rt2)/sel(dept=10).
  sel(Rt1/2_0:dept=10) can be estimated if we know the cardinality #r1_0 of
  the range for sub-index idx1_0 (dept) of the index idx1 or the cardinality
  #rt2_0 of the same range for sub-index idx2_0(dept) of the index idx2.
  The current code does not make an estimate either for #rt1_0, or for #rt2_0,
  but it can be adjusted to provide those numbers.
  Alternatively, MY_MIN(rec_per_key) for (dept) could be used to get an upper 
  bound for the value of sel(Rt1&Rt2). Yet this statistics is not provided
  now.  
 
  Let's consider two other indexes idx1:(dept, last_name), 
  idx2:(first_name, last_name) and two range conditions over these indexes:
    Rt1: dept=5 AND last_name='Sm%'
    Rt2: first_name='Robert' AND last_name='Sm%'.

  sel(Rt1&Rt2)=sel(dept=5)*sel(last_name='Sm5')*sel(first_name='Robert')
  =sel(Rt2)*sel(dept=5)
  Here MY_MAX(rec_per_key) for (dept) could be used to get an upper bound for
  the value of sel(Rt1&Rt2).
  
  When the intersected indexes have different major columns, but some
  minor column are common the picture may be more complicated.

  Let's consider the following range conditions for the same indexes as in
  the previous example:
    Rt1: (Rt11: dept=5 AND last_name='So%') 
         OR 
         (Rt12: dept=7 AND last_name='Saw%')
    Rt2: (Rt21: first_name='Robert' AND last_name='Saw%')
         OR
         (Rt22: first_name='Bob' AND last_name='So%')
  Here we have:
  sel(Rt1&Rt2)= sel(Rt11)*sel(Rt21)+sel(Rt22)*sel(dept=5) +
                sel(Rt21)*sel(dept=7)+sel(Rt12)*sel(Rt22)
  Now consider the range condition:
    Rt1_0: (dept=5 OR dept=7)
  For this condition we can state that:
  sel(Rt1_0&Rt2)=(sel(dept=5)+sel(dept=7))*(sel(Rt21)+sel(Rt22))=
  sel(dept=5)*sel(Rt21)+sel(dept=7)*sel(Rt21)+
  sel(dept=5)*sel(Rt22)+sel(dept=7)*sel(Rt22)=
  sel(dept=5)*sel(Rt21)+sel(Rt21)*sel(dept=7)+
  sel(Rt22)*sel(dept=5)+sel(dept=7)*sel(Rt22) >
  sel(Rt11)*sel(Rt21)+sel(Rt22)*sel(dept=5)+
  sel(Rt21)*sel(dept=7)+sel(Rt12)*sel(Rt22) >
  sel(Rt1 & Rt2) 

 We've just demonstrated for an example what is intuitively almost obvious
 in general. We can  remove the ending parts fromrange trees getting less
 selective range conditions for sub-indexes.
 So if not a most major component with the number k of an index idx is
 encountered in the index with which we intersect we can use the sub-index
 idx_k-1 that includes the components of idx up to the i-th component and
 the range tree for idx_k-1 to make an upper bound estimate for the number
  of records in the index intersection.
 The range tree for idx_k-1 we use here is the subtree of the original range
  tree for idx that contains only parts from the first k-1 components.

  As it was mentioned above the range optimizer currently does not provide
  an estimate for the number of records in the ranges for sub-indexes.
  However, some reasonable upper bound estimate can be obtained.

  Let's consider the following range tree:
    Rt: (first_name='Robert' AND last_name='Saw%')
        OR
        (first_name='Bob' AND last_name='So%')
  Let #r be the number of records in Rt. Let f_1 be the fan-out of column
  last_name:
    f_1 = rec_per_key[first_name]/rec_per_key[last_name].
  The the number of records in the range tree:
    Rt_0:  (first_name='Robert' OR first_name='Bob')
  for the sub-index (first_name) is not greater than MY_MAX(#r*f_1, #t).
  Strictly speaking, we can state only that it's not greater than 
  MY_MAX(#r*max_f_1, #t), where
    max_f_1= max_rec_per_key[first_name]/min_rec_per_key[last_name].
  Yet, if #r/#t is big enough (and this is the case of an index intersection,
  because using this index range with a single index scan is cheaper than
  the cost of the intersection when #r/#t is small) then almost safely we
  can use here f_1 instead of max_f_1.

  The above considerations can be used in future development. Now, they are
  used partly in the function that provides a rough upper bound estimate for
  the number of records in an index intersection that follow below.
*/

/*
  Estimate the number of records selected by an extension a partial intersection

  SYNOPSIS
    records_in_index_intersect_extension()
     curr            partial intersection plan to be extended
     ext_index_scan  the evaluated extension of this partial plan

  DESCRIPTION
    The function provides an estimate for the number of records in the
    intersection of the partial index intersection curr with the index
    ext_index_scan. If all intersected indexes does not have common columns
    then  the function returns an exact estimate (assuming there are no
    correlations between values in the columns). If the intersected indexes
    have common  columns the function returns an upper bound for the number
    of records in the intersection provided that the intersection of curr
    with ext_index_scan can is expected to have less records than the expected
    number of records in the partial intersection curr. In this case the
    function also assigns the bitmap of the columns in the extended 
    intersection to ext_index_scan->used_fields.
    If the function cannot expect that the number of records in the extended
    intersection is less that the expected number of records #r in curr then
    the function returns a number bigger than #r.

  NOTES
   See the comment before the description of the function that explains the
   reasoning used  by this function.
    
  RETURN
    The expected number of rows in the extended index intersection
*/

static
ha_rows records_in_index_intersect_extension(PARTIAL_INDEX_INTERSECT_INFO *curr,
                                             INDEX_SCAN_INFO *ext_index_scan)
{
  KEY *key_info= ext_index_scan->key_info;
  KEY_PART_INFO* key_part= key_info->key_part;
  uint used_key_parts= ext_index_scan->used_key_parts;
  MY_BITMAP *used_fields= &ext_index_scan->used_fields;
  
  if (!curr->length)
  {
    /* 
      If this the first index in the intersection just mark the
      fields in the used_fields bitmap and return the expected
      number of records in the range scan for the index provided
      by the range optimizer.
    */ 
    set_field_bitmap_for_index_prefix(used_fields, key_part, used_key_parts);
    return ext_index_scan->records;
  }

  uint i;
  bool better_selectivity= FALSE;
  ha_rows records= curr->records;
  MY_BITMAP *curr_intersect_fields= curr->intersect_fields; 
  for (i= 0; i < used_key_parts; i++, key_part++)
  {
    if (bitmap_is_set(curr_intersect_fields, key_part->fieldnr-1))
      break;
  }
  if (i)
  {
    ha_rows table_cardinality= curr->common_info->table_cardinality;
    ha_rows ext_records= ext_index_scan->records;
    if (i < used_key_parts)
    {
      double f1= key_info->actual_rec_per_key(i-1);
      double f2= key_info->actual_rec_per_key(i);
      ext_records= (ha_rows) ((double) ext_records / f2 * f1);
    }
    if (ext_records < table_cardinality)
    {
      better_selectivity= TRUE;
      records= (ha_rows) ((double) records / table_cardinality *
			  ext_records);
      bitmap_copy(used_fields, curr_intersect_fields);
      key_part= key_info->key_part;
      for (uint j= 0; j < used_key_parts; j++, key_part++)
        bitmap_set_bit(used_fields, key_part->fieldnr-1);
    }
  }
  return !better_selectivity ? records+1 :
                               !records ? 1 : records;
}


/* 
  Estimate the cost a binary search within disjoint cpk range intervals

  Number of comparisons to check whether a cpk value satisfies
  the cpk range condition = log2(cpk_scan->range_count).
*/ 

static inline
double get_cpk_filter_cost(ha_rows filtered_records, 
                           INDEX_SCAN_INFO *cpk_scan,
                           double compare_factor)
{
  return (log((double) (cpk_scan->range_count+1)) * compare_factor / M_LN2 *
          filtered_records);
}


/*
  Check whether a partial index intersection plan can be extended

  SYNOPSIS
    check_index_intersect_extension()
     curr            partial intersection plan to be extended
     ext_index_scan  a possible extension of this plan to be checked
     next       OUT  the structure to be filled for the extended plan 

  DESCRIPTION
    The function checks whether it makes sense to extend the index
    intersection plan adding the index ext_index_scan, and, if this
    the case, the function fills in the structure for the extended plan.

  RETURN
    TRUE      if it makes sense to extend the given plan 
    FALSE     otherwise
*/

static
bool check_index_intersect_extension(THD *thd,
                                     PARTIAL_INDEX_INTERSECT_INFO *curr,
                                     INDEX_SCAN_INFO *ext_index_scan,
                                     PARTIAL_INDEX_INTERSECT_INFO *next)
{
  ha_rows records;
  ha_rows records_sent_to_unique;
  double cost;
  ha_rows ext_index_scan_records= ext_index_scan->records;
  ha_rows records_filtered_out_by_cpk= ext_index_scan->filtered_out;
  COMMON_INDEX_INTERSECT_INFO *common_info= curr->common_info;
  double cutoff_cost= common_info->cutoff_cost;
  uint idx= curr->length;
  Json_writer_object trace(thd, "check_index_intersect_extension");

  next->index_read_cost= curr->index_read_cost+ext_index_scan->index_read_cost;
  if (next->index_read_cost > cutoff_cost)
  {
    if (unlikely(trace.trace_started()))
      trace.
        add("index", ext_index_scan->key_info->name.str).
        add("cost", next->index_read_cost).
        add("chosen", false).
        add("cause", "cost");
    return FALSE;
  }

  if ((next->in_memory= curr->in_memory))
    next->in_memory_cost= curr->in_memory_cost;

  next->intersect_fields= &ext_index_scan->used_fields;
  next->filtered_scans= curr->filtered_scans;

  records_sent_to_unique= curr->records_sent_to_unique;

  next->use_cpk_filter= FALSE;

  /* Calculate the cost of using a Unique object for index intersection */
  if (idx && next->in_memory)
  { 
    /* 
      All rowids received from the first scan are expected in one unique tree
    */
    ha_rows elems_in_tree= common_info->search_scans[0]->records-
                           common_info->search_scans[0]->filtered_out ;
    next->in_memory_cost+= Unique::get_search_cost(elems_in_tree,
                                                   common_info->compare_factor)* 
                             ext_index_scan_records;
    cost= next->in_memory_cost;

  }
  else
  {
    uint *buff_elems= common_info->buff_elems;
    uint key_size= common_info->key_size;
    double compare_factor= common_info->compare_factor;
    size_t max_memory_size= common_info->max_memory_size;

    records_sent_to_unique+= ext_index_scan_records;
    cost= Unique::get_use_cost(thd, buff_elems, (size_t) records_sent_to_unique,
                               key_size,
                               max_memory_size, compare_factor, TRUE,
                               &next->in_memory);
    if (records_filtered_out_by_cpk)
    {
      /* Check whether using cpk filter for this scan is beneficial */

      double cost2;
      bool in_memory2;
      ha_rows records2= records_sent_to_unique-records_filtered_out_by_cpk;
      cost2=  Unique::get_use_cost(thd, buff_elems, (size_t) records2, key_size,
                                   max_memory_size, compare_factor, TRUE,
                                   &in_memory2);
      cost2+= get_cpk_filter_cost(ext_index_scan_records, common_info->cpk_scan,
                                  compare_factor);
      if (cost > cost2 + COST_EPS)
      {
        cost= cost2;
        next->in_memory= in_memory2;
        next->use_cpk_filter= TRUE;
        records_sent_to_unique= records2;
      }

    }   
    if (next->in_memory)
      next->in_memory_cost= cost;
  }
  if (unlikely(trace.trace_started()))
  {
    trace.
      add("index", ext_index_scan->key_info->name.str).
      add("in_memory", next->in_memory).
      add("range_rows", ext_index_scan_records).
      add("rows_sent_to_unique", records_sent_to_unique).
      add("unique_cost", cost).
      add("index_read_cost", next->index_read_cost);
    if (next->use_cpk_filter)
      trace.add("rows_filtered_out_by_clustered_pk", records_filtered_out_by_cpk);
  }


  if (next->use_cpk_filter)
  {
    next->filtered_scans.set_bit(ext_index_scan->keynr);
    bitmap_union(&ext_index_scan->used_fields,
                 &common_info->cpk_scan->used_fields);
  }
  next->records_sent_to_unique= records_sent_to_unique;
       
  records= records_in_index_intersect_extension(curr, ext_index_scan);
  if (idx && records > curr->records)
  {
    if (unlikely(trace.trace_started()))
      trace.
        add("rows", records).
        add("chosen", false).
        add("cause", "too many rows");
    return FALSE;
  }
  if (next->use_cpk_filter && curr->filtered_scans.is_clear_all())
    records-= records_filtered_out_by_cpk;
  next->records= records;

  cost+= next->index_read_cost;
  if (cost >= cutoff_cost)
  {
    if (unlikely(trace.trace_started()))
      trace.add("cost", cost).add("chosen", false).add("cause", "cost");
    return FALSE;
  }

  /*
    The cost after sweep can be bigger than cutoff, but that is ok as the
    end cost can decrease when we add the next index.
  */
  cost+= get_sweep_read_cost(common_info->param, rows2double(records), 1);

  next->cost= cost;
  next->length= curr->length+1;

  if (unlikely(trace.trace_started()))
    trace.add("rows", records).add("cost", cost).add("chosen", true);
  return TRUE;
}


/*
  Search for the cheapest extensions of range scans used to access a table    

  SYNOPSIS
    find_index_intersect_best_extension()
      curr        partial intersection to evaluate all possible extension for 

  DESCRIPTION
    The function tries to extend the partial plan curr in all possible ways
    to look for a cheapest index intersection whose cost less than the 
    cut off value set in curr->common_info.cutoff_cost. 
*/

static 
void find_index_intersect_best_extension(THD *thd,
                                         PARTIAL_INDEX_INTERSECT_INFO *curr)
{
  PARTIAL_INDEX_INTERSECT_INFO next;
  COMMON_INDEX_INTERSECT_INFO *common_info= curr->common_info;
  INDEX_SCAN_INFO **index_scans= common_info->search_scans;
  uint idx= curr->length;
  INDEX_SCAN_INFO **rem_first_index_scan_ptr= &index_scans[idx];
  double cost= curr->cost;

  if (cost + COST_EPS < common_info->best_cost)
  {
    common_info->best_cost= cost;
    common_info->best_length= curr->length;
    common_info->best_records= curr->records;
    common_info->filtered_scans= curr->filtered_scans;
    /* common_info->best_uses_cpk <=> at least one scan uses a cpk filter */
    common_info->best_uses_cpk= !curr->filtered_scans.is_clear_all();
    uint sz= sizeof(INDEX_SCAN_INFO *) * curr->length;
    memcpy(common_info->best_intersect, common_info->search_scans, sz);
    common_info->cutoff_cost= cost;
  }   

  if (!(*rem_first_index_scan_ptr))
    return;  

  next.common_info= common_info;
 
  Json_writer_array potential_index_intersect(thd, "potential_index_intersect");

  INDEX_SCAN_INFO *rem_first_index_scan= *rem_first_index_scan_ptr;
  for (INDEX_SCAN_INFO **index_scan_ptr= rem_first_index_scan_ptr;
       *index_scan_ptr; index_scan_ptr++)
  {
    Json_writer_object selected(thd);
    *rem_first_index_scan_ptr= *index_scan_ptr;
    *index_scan_ptr= rem_first_index_scan;
    if (check_index_intersect_extension(thd, curr, *rem_first_index_scan_ptr,
                                        &next))
      find_index_intersect_best_extension(thd, &next);
    *index_scan_ptr= *rem_first_index_scan_ptr;
    *rem_first_index_scan_ptr= rem_first_index_scan;
  }
}


/*
  Get the plan of the best intersection of range scans used to access a table    

  SYNOPSIS
    get_best_index_intersect()
      param         common info about index ranges
      tree          tree of ranges for indexes that can be intersected
      read_time     cut off value for the evaluated plans 

  DESCRIPTION
    The function looks for the cheapest index intersection of the range
    scans to access a table. The info about the ranges for all indexes
    is provided by the range optimizer and is passed through the
    parameters param and tree. Any plan whose cost is greater than read_time
    is rejected. 
    After the best index intersection is found the function constructs
    the structure that manages the execution by the chosen plan.

  RETURN
    Pointer to the generated execution structure if a success,
    0 - otherwise.
*/

static
TRP_INDEX_INTERSECT *get_best_index_intersect(PARAM *param, SEL_TREE *tree,
                                              double read_time)
{
  uint i;
  uint count;
  TRP_RANGE **cur_range;
  TRP_RANGE **range_scans;
  INDEX_SCAN_INFO *index_scan;
  COMMON_INDEX_INTERSECT_INFO common;
  PARTIAL_INDEX_INTERSECT_INFO init;
  TRP_INDEX_INTERSECT *intersect_trp= NULL;
  TABLE *table= param->table;
  THD *thd= param->thd;
  DBUG_ENTER("get_best_index_intersect");

  Json_writer_object trace_idx_interect(thd, "analyzing_sort_intersect");

  if (unlikely(trace_idx_interect.trace_started()))
    trace_idx_interect.add("cutoff_cost", read_time);

  if (prepare_search_best_index_intersect(param, tree, &common, &init,
                                          read_time))
    DBUG_RETURN(NULL);

  find_index_intersect_best_extension(thd, &init);

  if (common.best_length <= 1 && !common.best_uses_cpk)
    DBUG_RETURN(NULL);

  if (common.best_uses_cpk)
  {
    memmove((char *) (common.best_intersect+1), (char *) common.best_intersect,
            sizeof(INDEX_SCAN_INFO *) * common.best_length);
    common.best_intersect[0]= common.cpk_scan;
    common.best_length++;
  }

  count= common.best_length;

  if (!(range_scans= (TRP_RANGE**)alloc_root(param->mem_root,
                                            sizeof(TRP_RANGE *)*
                                            count)))
    DBUG_RETURN(NULL);

  for (i= 0, cur_range= range_scans; i < count; i++)
  {
    index_scan= common.best_intersect[i];
    if ((*cur_range= new (param->mem_root) TRP_RANGE(index_scan->sel_arg,
                                                     index_scan->idx, 0)))
    {  
      TRP_RANGE *trp= *cur_range;  
      trp->read_cost= index_scan->index_read_cost;  
      trp->records= index_scan->records;        
      trp->is_ror= FALSE;
      trp->mrr_buf_size= 0;
      table->intersect_keys.set_bit(index_scan->keynr);
      cur_range++;
    }
  }
  
  count= (uint)(tree->index_scans_end - tree->index_scans);
  for (i= 0; i < count; i++)
  {
    index_scan= tree->index_scans[i]; 
    if (!table->intersect_keys.is_set(index_scan->keynr))
    {
      for (uint j= 0; j < common.best_length; j++)
      {
	INDEX_SCAN_INFO *scan= common.best_intersect[j];
        if (same_index_prefix(index_scan->key_info, scan->key_info,
                              scan->used_key_parts))
	{
          table->intersect_keys.set_bit(index_scan->keynr);
          break;
        } 
      }
    }
  }
      
  if ((intersect_trp= new (param->mem_root)TRP_INDEX_INTERSECT))
  {

    intersect_trp->read_cost= common.best_cost;
    intersect_trp->records=   common.best_records;
    intersect_trp->range_scans= range_scans;
    intersect_trp->range_scans_end= cur_range;
    intersect_trp->filtered_scans= common.filtered_scans;
    if (unlikely(trace_idx_interect.trace_started()))
      trace_idx_interect.
        add("rows", intersect_trp->records).
        add("cost", intersect_trp->read_cost).
        add("chosen",true);
  }
  DBUG_RETURN(intersect_trp);
}


typedef struct st_ror_scan_info : INDEX_SCAN_INFO
{ 
} ROR_SCAN_INFO;

void TRP_ROR_INTERSECT::trace_basic_info(PARAM *param,
                                         Json_writer_object *trace_object) const
{
  THD *thd= param->thd;
  DBUG_ASSERT(trace_object->trace_started());

  trace_object->
    add("type", "index_roworder_intersect").
    add("rows", records).
    add("cost", read_cost).
    add("covering", is_covering).
    add("clustered_pk_scan", cpk_scan != NULL);

  Json_writer_array smth_trace(thd, "intersect_of");
  for (ROR_SCAN_INFO **cur_scan= first_scan; cur_scan != last_scan;
                                                         cur_scan++)
  {
    const KEY &cur_key= param->table->key_info[(*cur_scan)->keynr];
    const KEY_PART_INFO *key_part= cur_key.key_part;

    Json_writer_object trace_isect_idx(thd);
    trace_isect_idx.
      add("type", "range_scan").
      add("index", cur_key.name).
      add("rows", (*cur_scan)->records);

    Json_writer_array trace_range(thd, "ranges");

    trace_ranges(&trace_range, param, (*cur_scan)->idx,
                 (*cur_scan)->sel_arg, key_part);
  }
}


/*
  Create ROR_SCAN_INFO* structure with a single ROR scan on index idx using
  sel_arg set of intervals.

  SYNOPSIS
    make_ror_scan()
      param    Parameter from test_quick_select function
      idx      Index of key in param->keys
      sel_arg  Set of intervals for a given key

  RETURN
    NULL - out of memory
    ROR scan structure containing a scan for {idx, sel_arg}
*/

static
ROR_SCAN_INFO *make_ror_scan(const PARAM *param, int idx, SEL_ARG *sel_arg)
{
  ROR_SCAN_INFO *ror_scan;
  my_bitmap_map *bitmap_buf;
  uint keynr;
  handler *file= param->table->file;
  DBUG_ENTER("make_ror_scan");

  if (!(ror_scan= (ROR_SCAN_INFO*)alloc_root(param->mem_root,
                                             sizeof(ROR_SCAN_INFO))))
    DBUG_RETURN(NULL);

  ror_scan->idx= idx;
  ror_scan->keynr= keynr= param->real_keynr[idx];
  ror_scan->key_rec_length= (param->table->key_info[keynr].key_length +
                             file->ref_length);
  ror_scan->sel_arg= sel_arg;
  ror_scan->records= param->quick_rows[keynr];

  if (!(bitmap_buf= (my_bitmap_map*) alloc_root(param->mem_root,
                                                param->fields_bitmap_size)))
    DBUG_RETURN(NULL);

  if (my_bitmap_init(&ror_scan->covered_fields, bitmap_buf,
                  param->table->s->fields))
    DBUG_RETURN(NULL);
  bitmap_clear_all(&ror_scan->covered_fields);

  KEY_PART_INFO *key_part= param->table->key_info[keynr].key_part;
  KEY_PART_INFO *key_part_end= key_part +
                               param->table->key_info[keynr].user_defined_key_parts;
  for (;key_part != key_part_end; ++key_part)
  {
    if (bitmap_is_set(&param->needed_fields, key_part->fieldnr-1))
      bitmap_set_bit(&ror_scan->covered_fields, key_part->fieldnr-1);
  }

  /*
    Cost of reading the keys for the rows, which are later stored in the
    ror queue.
  */
  ror_scan->index_read_cost=
    file->cost(file->ha_keyread_and_copy_time(ror_scan->keynr, 1,
                                              ror_scan->records, 0));
  DBUG_RETURN(ror_scan);
}


/*
  Compare two ROR_SCAN_INFO** by  E(#records_matched) * key_record_length.
  SYNOPSIS
    cmp_ror_scan_info()
      a ptr to first compared value
      b ptr to second compared value

  RETURN
   -1 a < b
    0 a = b
    1 a > b
*/

static int cmp_ror_scan_info(const void *a_, const void *b_)
{
  auto a= static_cast<const ROR_SCAN_INFO *const *>(a_);
  auto b= static_cast<const ROR_SCAN_INFO *const *>(b_);
  double val1= rows2double((*a)->records) * (*a)->key_rec_length;
  double val2= rows2double((*b)->records) * (*b)->key_rec_length;
  return (val1 < val2)? -1: (val1 == val2)? 0 : 1;
}

/*
  Compare two ROR_SCAN_INFO** by
   (#covered fields in F desc,
    #components asc,
    number of first not covered component asc)

  SYNOPSIS
    cmp_ror_scan_info_covering()
      a ptr to first compared value
      b ptr to second compared value

  RETURN
   -1 a < b
    0 a = b
    1 a > b
*/

static int cmp_ror_scan_info_covering(const void *a_, const void *b_)
{
  auto a= static_cast<const ROR_SCAN_INFO *const *>(a_);
  auto b= static_cast<const ROR_SCAN_INFO *const *>(b_);
  if ((*a)->used_fields_covered > (*b)->used_fields_covered)
    return -1;
  if ((*a)->used_fields_covered < (*b)->used_fields_covered)
    return 1;
  if ((*a)->key_components < (*b)->key_components)
    return -1;
  if ((*a)->key_components > (*b)->key_components)
    return 1;
  if ((*a)->first_uncovered_field < (*b)->first_uncovered_field)
    return -1;
  if ((*a)->first_uncovered_field > (*b)->first_uncovered_field)
    return 1;
  return 0;
}


/* Auxiliary structure for incremental ROR-intersection creation */
typedef struct
{
  const PARAM *param;
  MY_BITMAP covered_fields; /* union of fields covered by all scans */
  /*
    Fraction of table records that satisfies conditions of all scans.
    This is the number of full records that will be retrieved if a
    non-index_only index intersection will be employed.
  */
  double out_rows;
  /* TRUE if covered_fields is a superset of needed_fields */
  bool is_covering;

  ha_rows index_records; /* sum(#records to look in indexes) */
  double index_scan_costs; /* SUM(cost of 'index-only' scans) */
  double total_cost;
  uint num_scans;  // Number of ROR scans that contributed to this intersection
} ROR_INTERSECT_INFO;


/*
  Allocate a ROR_INTERSECT_INFO and initialize it to contain zero scans.

  SYNOPSIS
    ror_intersect_init()
      param         Parameter from test_quick_select

  RETURN
    allocated structure
    NULL on error
*/

static
ROR_INTERSECT_INFO* ror_intersect_init(const PARAM *param)
{
  ROR_INTERSECT_INFO *info;
  my_bitmap_map* buf;
  if (!(info= (ROR_INTERSECT_INFO*)alloc_root(param->mem_root,
                                              sizeof(ROR_INTERSECT_INFO))))
    return NULL;
  info->param= param;
  if (!(buf= (my_bitmap_map*) alloc_root(param->mem_root,
                                         param->fields_bitmap_size)))
    return NULL;
  if (my_bitmap_init(&info->covered_fields, buf, param->table->s->fields))
    return NULL;
  info->is_covering= FALSE;
  info->index_scan_costs= 0.0;
  info->index_records= 0;
  info->out_rows= (double) param->table->stat_records();
  info->num_scans= 0;
  bitmap_clear_all(&info->covered_fields);
  return info;
}

void ror_intersect_cpy(ROR_INTERSECT_INFO *dst, const ROR_INTERSECT_INFO *src)
{
  dst->param= src->param;
  bitmap_copy(&dst->covered_fields, &src->covered_fields);
  dst->out_rows= src->out_rows;
  dst->is_covering= src->is_covering;
  dst->index_records= src->index_records;
  dst->index_scan_costs= src->index_scan_costs;
  dst->total_cost= src->total_cost;
  dst->num_scans= src->num_scans;
}


/*
  Get selectivity of a ROR scan wrt ROR-intersection.

  SYNOPSIS
    ror_scan_selectivity()
      info  ROR-interection 
      scan  ROR scan
      
  NOTES
    Suppose we have a condition on several keys
    cond=k_11=c_11 AND k_12=c_12 AND ...  // parts of first key
         k_21=c_21 AND k_22=c_22 AND ...  // parts of second key
          ...
         k_n1=c_n1 AND k_n3=c_n3 AND ...  (1) //parts of the key used by *scan

    where k_ij may be the same as any k_pq (i.e. keys may have common parts).

    A full row is retrieved if entire condition holds.

    The recursive procedure for finding P(cond) is as follows:

    First step:
    Pick 1st part of 1st key and break conjunction (1) into two parts:
      cond= (k_11=c_11 AND R)

    Here R may still contain condition(s) equivalent to k_11=c_11.
    Nevertheless, the following holds:

      P(k_11=c_11 AND R) = P(k_11=c_11) * P(R | k_11=c_11).

    Mark k_11 as fixed field (and satisfied condition) F, save P(F),
    save R to be cond and proceed to recursion step.

    Recursion step:
    We have a set of fixed fields/satisfied conditions) F, probability P(F),
    and remaining conjunction R
    Pick next key part on current key and its condition "k_ij=c_ij".
    We will add "k_ij=c_ij" into F and update P(F).
    Lets denote k_ij as t,  R = t AND R1, where R1 may still contain t. Then

     P((t AND R1)|F) = P(t|F) * P(R1|t|F) = P(t|F) * P(R1|(t AND F)) (2)

    (where '|' mean conditional probability, not "or")

    Consider the first multiplier in (2). One of the following holds:
    a) F contains condition on field used in t (i.e. t AND F = F).
      Then P(t|F) = 1

    b) F doesn't contain condition on field used in t. Then F and t are
     considered independent.

     P(t|F) = P(t|(fields_before_t_in_key AND other_fields)) =
          = P(t|fields_before_t_in_key).

     P(t|fields_before_t_in_key) = #records(fields_before_t_in_key) /
                                   #records(fields_before_t_in_key, t)

    The second multiplier is calculated by applying this step recursively.

  IMPLEMENTATION
    This function calculates the result of application of the "recursion step"
    described above for all fixed key members of a single key, accumulating set
    of covered fields, selectivity, etc.

    The calculation is conducted as follows:
    Lets denote #records(keypart1, ... keypartK) as n_k. We need to calculate

     n_{k1}      n_{k2}
    --------- * ---------  * .... (3)
     n_{k1-1}    n_{k2-1}

    where k1,k2,... are key parts which fields were not yet marked as fixed
    ( this is result of application of option b) of the recursion step for
      parts of a single key).
    Since it is reasonable to expect that most of the fields are not marked
    as fixed, we calculate (3) as

                                  n_{i1}      n_{i2}
    (3) = n_{max_key_part}  / (   --------- * ---------  * ....  )
                                  n_{i1-1}    n_{i2-1}

    where i1,i2, .. are key parts that were already marked as fixed.

    In order to minimize number of expensive records_in_range calls we group
    and reduce adjacent fractions.

  RETURN
    Selectivity of given ROR scan.
*/

static double ror_scan_selectivity(const ROR_INTERSECT_INFO *info, 
                                   const ROR_SCAN_INFO *scan)
{
  double selectivity_mult= 1.0;
  KEY_PART_INFO *key_part= info->param->table->key_info[scan->keynr].key_part;
  uchar key_val[MAX_KEY_LENGTH+MAX_FIELD_WIDTH]; /* key values tuple */
  uchar *key_ptr= key_val;
  SEL_ARG *sel_arg, *tuple_arg= NULL;
  key_part_map keypart_map= 0;
  bool cur_covered;
  bool prev_covered= MY_TEST(bitmap_is_set(&info->covered_fields,
                                           key_part->fieldnr - 1));
  key_range min_range;
  key_range max_range;
  min_range.key= key_val;
  min_range.flag= HA_READ_KEY_EXACT;
  max_range.key= key_val;
  max_range.flag= HA_READ_AFTER_KEY;
  ha_rows prev_records= info->param->table->stat_records();
  DBUG_ENTER("ror_scan_selectivity");

  for (sel_arg= scan->sel_arg; sel_arg;
       sel_arg= sel_arg->next_key_part)
  {
    DBUG_PRINT("info",("sel_arg step"));
    cur_covered= MY_TEST(bitmap_is_set(&info->covered_fields,
                                       key_part[sel_arg->part].fieldnr - 1));
    if (cur_covered != prev_covered)
    {
      /* create (part1val, ..., part{n-1}val) tuple. */
      ha_rows records;
      page_range pages;
      if (!tuple_arg)
      {
        tuple_arg= scan->sel_arg;
        /* Here we use the length of the first key part */
        tuple_arg->store_min(key_part->store_length, &key_ptr, 0);
        keypart_map= 1;
      }
      while (tuple_arg->next_key_part != sel_arg)
      {
        tuple_arg= tuple_arg->next_key_part;
        tuple_arg->store_min(key_part[tuple_arg->part].store_length,
                             &key_ptr, 0);
        keypart_map= (keypart_map << 1) | 1;
      }
      min_range.length= max_range.length= (uint) (key_ptr - key_val);
      min_range.keypart_map= max_range.keypart_map= keypart_map;
      records= (info->param->table->file->
                records_in_range(scan->keynr, &min_range, &max_range, &pages));
      if (cur_covered)
      {
        /* uncovered -> covered */
        double tmp= rows2double(records)/rows2double(prev_records);
        DBUG_PRINT("info", ("Selectivity multiplier: %g", tmp));
        selectivity_mult *= tmp;
        prev_records= HA_POS_ERROR;
      }
      else
      {
        /* covered -> uncovered */
        prev_records= records;
      }
    }
    prev_covered= cur_covered;
  }
  if (!prev_covered)
  {
    double tmp= rows2double(info->param->quick_rows[scan->keynr]) /
                rows2double(prev_records);
    DBUG_PRINT("info", ("Selectivity multiplier: %g", tmp));
    selectivity_mult *= tmp;
  }
  DBUG_PRINT("info", ("Returning multiplier: %g", selectivity_mult));
  DBUG_RETURN(selectivity_mult);
}


/*
  Check if adding a ROR scan to a ROR-intersection reduces its cost of
  ROR-intersection and if yes, update parameters of ROR-intersection,
  including its cost.

  SYNOPSIS
    ror_intersect_add()
      param        Parameter from test_quick_select
      info         ROR-intersection structure to add the scan to.
      ror_scan     ROR scan info to add.
      is_cpk_scan  If TRUE, add the scan as CPK scan (this can be inferred
                   from other parameters and is passed separately only to
                   avoid duplicating the inference code)

  NOTES
    Adding a ROR scan to ROR-intersect "makes sense" if the cost of ROR-
    intersection decreases. The cost of ROR-intersection is calculated as
    follows:

    cost= SUM_i(key_scan_cost_i) + cost_of_full_rows_retrieval

    When we add a scan the first increases and the second decreases.

    cost_of_full_rows_retrieval=
      (union of indexes used covers all needed fields) ?
        cost_of_sweep_read(E(rows_to_retrieve), rows_in_table) :
        0

    E(rows_to_retrieve) = #rows_in_table * ror_scan_selectivity(null, scan1) *
                           ror_scan_selectivity({scan1}, scan2) * ... *
                           ror_scan_selectivity({scan1,...}, scanN). 
  RETURN
    TRUE   ROR scan added to ROR-intersection, cost updated.
    FALSE  It doesn't make sense to add this ROR scan to this ROR-intersection.
*/

static bool ror_intersect_add(ROR_INTERSECT_INFO *info,
                              ROR_SCAN_INFO* ror_scan,
                              Json_writer_object *trace_costs,
                              bool is_cpk_scan,
                              bool ignore_cost)
{
  double selectivity_mult= 1.0;

  DBUG_ENTER("ror_intersect_add");
  DBUG_PRINT("info", ("Current out_rows= %g", info->out_rows));
  DBUG_PRINT("info", ("Adding scan on %s",
                      info->param->table->key_info[ror_scan->keynr].name.str));
  DBUG_PRINT("info", ("is_cpk_scan: %d",is_cpk_scan));

  selectivity_mult = ror_scan_selectivity(info, ror_scan);
  if (selectivity_mult == 1.0 && !ignore_cost)
  {
    /* Don't add this scan if it doesn't improve selectivity. */
    DBUG_PRINT("info", ("The scan doesn't improve selectivity."));
    DBUG_RETURN(FALSE);
  }

  info->out_rows *= selectivity_mult;
  
  if (is_cpk_scan)
  {
    /*
      CPK scan is used to filter out rows. We apply filtering for 
      each record of every scan. Assuming ROWID_COMPARE_COST
      per check this gives us:
    */
    const double idx_cost= (rows2double(info->index_records) *
                            ROWID_COMPARE_COST_THD(info->param->thd));
    info->index_scan_costs+= idx_cost;
    trace_costs->add("index_scan_cost", idx_cost);
  }
  else
  {
    info->index_records += info->param->quick_rows[ror_scan->keynr];
    info->index_scan_costs += ror_scan->index_read_cost;
    trace_costs->add("index_scan_cost", ror_scan->index_read_cost);
    bitmap_union(&info->covered_fields, &ror_scan->covered_fields);
    if (!info->is_covering && bitmap_is_subset(&info->param->needed_fields,
                                               &info->covered_fields))
    {
      DBUG_PRINT("info", ("ROR-intersect is covering now"));
      info->is_covering= TRUE;
    }
  }
  ++info->num_scans;

  info->total_cost= info->index_scan_costs;
  trace_costs->add("cumulated_index_scan_cost", info->index_scan_costs);
  DBUG_PRINT("info", ("info->total_cost: %g", info->total_cost));
  if (!info->is_covering)
  {
    double sweep_cost= get_sweep_read_cost(info->param, info->out_rows, 1);
    info->total_cost+= sweep_cost;
    trace_costs->add("disk_sweep_cost", sweep_cost);
    DBUG_PRINT("info", ("info->total_cost= %g", info->total_cost));
  }
  else
  {
    trace_costs->add("disk_sweep_cost", static_cast<longlong>(0));
  }

  DBUG_PRINT("info", ("New out_rows: %g", info->out_rows));
  DBUG_PRINT("info", ("New cost: %g, %scovering", info->total_cost,
                      info->is_covering?"" : "non-"));
  DBUG_RETURN(TRUE);
}


/*
  Get best ROR-intersection plan using non-covering ROR-intersection search
  algorithm. The returned plan may be covering.

  SYNOPSIS
    get_best_ror_intersect()
      param            Parameter from test_quick_select function.
      tree             Transformed restriction condition to be used to look
                       for ROR scans.
      read_time        Do not return read plans with cost > read_time.
      are_all_covering [out] set to TRUE if union of all scans covers all
                       fields needed by the query (and it is possible to build
                       a covering ROR-intersection)

  NOTES
    get_key_scans_params must be called before this function can be called.
    
    When this function is called by ROR-union construction algorithm it
    assumes it is building an uncovered ROR-intersection (and thus # of full
    records to be retrieved is wrong here). This is a hack.

  IMPLEMENTATION
    The approximate best non-covering plan search algorithm is as follows:

    find_min_ror_intersection_scan()
    {
      R= select all ROR scans;
      order R by (E(#records_matched) * key_record_length).

      S= first(R); -- set of scans that will be used for ROR-intersection
      R= R - S;
      min_cost= cost(S);
      min_scan= make_scan(S);
      while (R is not empty)
      {
        firstR= first(R);
        if (!selectivity(S + firstR) < selectivity(S))
        {
          R= R - firstR;
          continue;
        }
        S= S + first(R);
        if (cost(S) < min_cost)
        {
          min_cost= cost(S);
          min_scan= make_scan(S);
        }
        R= R - firstR; --  Remove the processed scan from R
      }
      return min_scan;
    }

    See ror_intersect_add function for ROR intersection costs.

    Special handling for Clustered PK scans
    Clustered PK contains all table fields, so using it as a regular scan in
    index intersection doesn't make sense: a range scan on CPK will be less
    expensive in this case.
    Clustered PK scan has special handling in ROR-intersection: it is not used
    to retrieve rows, instead its condition is used to filter row references
    we get from scans on other keys.

  RETURN
    ROR-intersection table read plan
    NULL if out of memory or no suitable plan found.
*/

static
TRP_ROR_INTERSECT *get_best_ror_intersect(const PARAM *param, SEL_TREE *tree,
                                          double read_time,
                                          bool *are_all_covering,
                                          bool force_index_merge_result)
{
  DBUG_ENTER("get_best_ror_intersect");
  DBUG_PRINT("enter", ("opt_range_condition_rows: %llu  cond_selectivity: %g",
                       (ulonglong) param->table->opt_range_condition_rows,
                       param->table->cond_selectivity));

  THD *thd= param->thd;
  Json_writer_object trace_ror(thd, "analyzing_roworder_intersect");

  bool force_index_merge=
    hint_table_state(thd,
                     param->table->pos_in_table_list,
                     INDEX_MERGE_HINT_ENUM, 0);

  if ((tree->n_ror_scans < 2) || !param->table->stat_records() ||
      (!optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT) &&
       !force_index_merge))
  {
    if (tree->n_ror_scans < 2)
      trace_ror.add("cause", "too few roworder scans");
    DBUG_RETURN(nullptr);
  }

  /*
    Step1: Collect ROR-able SEL_ARGs and create ROR_SCAN_INFO for each of
    them. Also find and save clustered PK scan if there is one.
  */
  if (!(tree->ror_scans= (ROR_SCAN_INFO**)alloc_root(param->mem_root,
                                                     sizeof(ROR_SCAN_INFO*)*
                                                     param->keys)))
    return nullptr;
  uint cpk_no= (param->table->file->
                pk_is_clustering_key(param->table->s->primary_key) ?
                param->table->s->primary_key : MAX_KEY);
  ROR_SCAN_INFO **cur_ror_scan= tree->ror_scans;
  ROR_SCAN_INFO *cpk_scan= nullptr;
  for (uint idx= 0; idx < param->keys; idx++)
  {
    ROR_SCAN_INFO *scan;
    uint key_no;
    if (!tree->ror_scans_map.is_set(idx))
      continue;
    key_no= param->real_keynr[idx];
    if (key_no != cpk_no && param->table->file->is_clustering_key(key_no))
    {
      /* Ignore clustering keys */
      tree->n_ror_scans--;
      continue;
    }
    if (!(scan= make_ror_scan(param, idx, tree->keys[idx])))
      return nullptr;
    if (key_no == cpk_no)
    {
      cpk_scan= scan;
      tree->n_ror_scans--;
    }
    else
      *(cur_ror_scan++)= scan;
  }

  tree->ror_scans_end= cur_ror_scan;
  DBUG_EXECUTE("info",print_ror_scans_arr(param->table, "original",
                                          tree->ror_scans,
                                          tree->ror_scans_end););
  /*
    Ok, [ror_scans, ror_scans_end) is array of ptrs to initialized
    ROR_SCAN_INFO's.
    Step 2: Get best ROR-intersection using an approximate algorithm.
  */
  my_qsort(tree->ror_scans, tree->n_ror_scans, sizeof(ROR_SCAN_INFO*),
           cmp_ror_scan_info);
  DBUG_EXECUTE("info",print_ror_scans_arr(param->table, "ordered",
                                          tree->ror_scans,
                                          tree->ror_scans_end););

  /*
    Create and incrementally update ROR intersection.
    [intersect_scans,intersect_scans_best) will hold the best intersection
  */
  ROR_SCAN_INFO **intersect_scans; /* ROR scans used in index intersection */
  if (!(intersect_scans= (ROR_SCAN_INFO**)alloc_root(param->mem_root,
                                                     sizeof(ROR_SCAN_INFO*)*
                                                     tree->n_ror_scans)))
    return nullptr;
  ROR_SCAN_INFO **intersect_scans_end= intersect_scans;
  ROR_SCAN_INFO **intersect_scans_best= intersect_scans;
  cur_ror_scan= tree->ror_scans;
  double min_cost= DBL_MAX;
  ROR_INTERSECT_INFO *intersect, *intersect_best;
  if (!(intersect= ror_intersect_init(param)) ||
      !(intersect_best= ror_intersect_init(param)))
    return nullptr;
  Json_writer_array trace_isect_idx(thd, "intersecting_indexes");
  bool use_cheapest_index_merge= false;
  while (cur_ror_scan != tree->ror_scans_end && !intersect->is_covering)
  {
    Json_writer_object trace_idx(thd);
    trace_idx.add("index",
                 param->table->key_info[(*cur_ror_scan)->keynr].name);

    const index_merge_behavior ihb= index_merge_hint(param->table,
                                                     (*cur_ror_scan)->keynr,
                                                     &force_index_merge,
                                                     &use_cheapest_index_merge);
    if (ihb == index_merge_behavior::USE_KEY)
      trace_idx.add("cause", "index_merge_hint");
    else if (ihb == index_merge_behavior::TABLE_DISABLED)
      DBUG_RETURN(nullptr);
    else if (ihb == index_merge_behavior::SKIP_KEY)
    {
      trace_idx.add("usable", false).add("cause", "index_merge_hint");
      cur_ror_scan++;
      continue;
    }

    /* S= S + first(R);  R= R - first(R); */
    if (!ror_intersect_add(intersect, *cur_ror_scan, &trace_idx, FALSE,
                           force_index_merge && !use_cheapest_index_merge))
    {
      trace_idx.
        add("usable", false).
        add("cause", "does not reduce cost of intersect");
      cur_ror_scan++;
      continue;
    }

    trace_idx.
      add("cumulative_total_cost", intersect->total_cost).
      add("usable", true).
      add("matching_rows_now", intersect->out_rows).
      add("intersect_covering_with_this_index", intersect->is_covering);

    *(intersect_scans_end++)= *(cur_ror_scan++);

    /*
      Check if intersect gives a lower cost.
      The first ror scan is always accepted.
      The next ror scan is only accepted if the total cost went down
      (Enough rows where reject to offset the intersect cost)
    */
    if (intersect->total_cost < min_cost ||
        (force_index_merge &&
         /*
           If INDEX_MERGE hint is used without any specified index,
           index merge is forced and the cheapest combination of indexes
           will be chosen. Since ranges are sorted by index scan cost,
           index merge is forced for first two ranges and next ranges are
           added only if they reduce total cost and there is no clustered
           primary key scan or intersection is covering. If there is
           a range by clustered primary key and intersection is not covering,
           combination of first index and primary key is considered as
           a cheapest intersection.
         */
         ((intersect_best->num_scans < 2 && force_index_merge_result &&
           (!cpk_scan || intersect->is_covering)) ||
          !use_cheapest_index_merge)))
    {
      /* Local minimum found, save it */
      min_cost= intersect->total_cost;
      ror_intersect_cpy(intersect_best, intersect);
      intersect_scans_best= intersect_scans_end;
      trace_idx.add("chosen", true);
    }
    else
    {
      trace_idx.
        add("chosen", false).
        add("cause", "does not reduce cost");
    }
  }
  trace_isect_idx.end();

  const uint num_scans= intersect_best->num_scans;
  if (intersect_scans_best == intersect_scans)
  {
    DBUG_PRINT("info", ("None of scans increase selectivity"));
    trace_ror.
      add("chosen", false).
      add("cause","does not increase selectivity");
    DBUG_RETURN(nullptr);
  }

  DBUG_EXECUTE("info",print_ror_scans_arr(param->table,
                                          "best ROR-intersection",
                                          intersect_scans,
                                          intersect_scans_best););

  *are_all_covering= intersect->is_covering;
  uint best_num= (uint) (intersect_scans_best - intersect_scans);
  DBUG_ASSERT(best_num <= tree->n_ror_scans);
  ror_intersect_cpy(intersect, intersect_best);

  /*
    Ok, found the best ROR-intersection of non-CPK key scans.
    Check if we should add a CPK scan. If the obtained ROR-intersection is
    covering, it doesn't make sense to add CPK scan.
  */
  Json_writer_object trace_cpk(thd, "clustered_pk");
  bool cpk_merge_allowed= false;
  if (cpk_scan)
  {
    const index_merge_behavior ihb= index_merge_hint(param->table,
                                                     cpk_scan->keynr);
    cpk_merge_allowed= (ihb == index_merge_behavior::USE_KEY ||
                        ihb == index_merge_behavior::TABLE_ENABLED ||
                        ihb == index_merge_behavior::NO_HINT);
  }

  if (cpk_merge_allowed && !intersect->is_covering)
  {
    if (ror_intersect_add(intersect, cpk_scan, &trace_cpk, TRUE, true) &&
        ((intersect->total_cost < min_cost) ||
         (force_index_merge &&
          (!use_cheapest_index_merge ||
           (num_scans == 1 && force_index_merge_result)))))
    {
      min_cost= intersect->total_cost;
      if (trace_cpk.trace_started())
        trace_cpk.
          add("clustered_pk_scan_added_to_intersect", true).
          add("cumulated_cost", intersect->total_cost);
      intersect_best= intersect; // just set pointer here
    }
    else
    {
      if (trace_cpk.trace_started())
        trace_cpk.
          add("clustered_pk_added_to_intersect", false).
          add("cause", "cost");
      cpk_scan= 0; // Don't use cpk_scan
    }
  }
  else
  {
    trace_cpk.
      add("clustered_pk_added_to_intersect", false).
      add("cause", cpk_scan ? "roworder is covering"
          : "no clustered pk index");
    cpk_scan= 0;                                // Don't use cpk_scan
  }
  trace_cpk.end();

  /*
    Adjust row count and add the cost of comparing the final rows to the
    WHERE clause
  */
  double cmp_cost= intersect_best->out_rows * thd->variables.optimizer_where_cost;

  /* Ok, return ROR-intersect plan if we have found one */
  TRP_ROR_INTERSECT *trp= nullptr;
  if ((min_cost + cmp_cost < read_time || force_index_merge) &&
      (cpk_scan || num_scans > 1))
  {
    double best_rows= intersect_best->out_rows;
    set_if_bigger(best_rows, 1);
    if (!(trp= new (param->mem_root) TRP_ROR_INTERSECT))
      DBUG_RETURN(nullptr);
    if (!(trp->first_scan=
           (ROR_SCAN_INFO**)alloc_root(param->mem_root,
                                       sizeof(ROR_SCAN_INFO*)*best_num)))
      DBUG_RETURN(nullptr);
    memcpy(trp->first_scan, intersect_scans, best_num*sizeof(ROR_SCAN_INFO*));
    trp->force_index_merge= force_index_merge;
    trp->last_scan=  trp->first_scan + best_num;
    trp->is_covering= intersect_best->is_covering;
    trp->read_cost= min_cost + cmp_cost;
    param->table->set_opt_range_condition_rows((ha_rows)best_rows);
    trp->records= (ha_rows)best_rows;
    trp->index_scan_costs= intersect_best->index_scan_costs;
    trp->cpk_scan= cpk_scan;
    DBUG_PRINT("info", ("Returning non-covering ROR-intersect plan:"
                        "cost %g, records %lu",
                        trp->read_cost, (ulong) trp->records));
    if (unlikely(trace_ror.trace_started()))
      trace_ror.
        add("rows",      trp->records).
        add("cost",     trp->read_cost).
        add("covering", trp->is_covering).
        add("chosen",   true);
  }
  else
  {
    trace_ror.
      add("chosen", false).
      add("cause", (min_cost + cmp_cost >= read_time) ?
          "cost" : "too few indexes to merge");
  }
  DBUG_PRINT("exit", ("opt_range_condition_rows: %llu",
                      (ulonglong) param->table->opt_range_condition_rows));
  DBUG_RETURN(trp);
}


/*
  Get best covering ROR-intersection.
  SYNOPSIS
    get_best_ntersectcovering_ror_intersect()
      param     Parameter from test_quick_select function.
      tree      SEL_TREE with sets of intervals for different keys.
      read_time Don't return table read plans with cost > read_time.
      force_index_merge Hint or optimizer switch mandates result.

  RETURN
    Best covering ROR-intersection plan
    NULL if no plan found.

  NOTES
    get_best_ror_intersect must be called for a tree before calling this
    function for it.
    This function invalidates tree->ror_scans member values.

  The following approximate algorithm is used:
    I=set of all covering indexes
    F=set of all fields to cover
    S={}

    do
    {
      Order I by (#covered fields in F desc,
                  #components asc,
                  number of first not covered component asc);
      F=F-covered by first(I);
      S=S+first(I);
      I=I-first(I);
    } while F is not empty.
*/

static
TRP_ROR_INTERSECT *get_best_covering_ror_intersect(PARAM *param,
                                                   SEL_TREE *tree,
                                                   double read_time,
                                                   bool force_index_merge)
{
  ROR_SCAN_INFO **ror_scan_mark;
  ROR_SCAN_INFO **ror_scans_end= tree->ror_scans_end;
  DBUG_ENTER("get_best_covering_ror_intersect");

  if (!optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_INTERSECT) &&
      !force_index_merge)
    DBUG_RETURN(NULL);

  for (ROR_SCAN_INFO **scan= tree->ror_scans; scan != ror_scans_end; ++scan)
    (*scan)->key_components=
      param->table->key_info[(*scan)->keynr].user_defined_key_parts;

  /*
    Run covering-ROR-search algorithm.
    Assume set I is [ror_scan .. ror_scans_end)
  */

  /*I=set of all covering indexes */
  ror_scan_mark= tree->ror_scans;

  MY_BITMAP *covered_fields= &param->tmp_covered_fields;
  if (!covered_fields->bitmap) 
    covered_fields->bitmap= (my_bitmap_map*)alloc_root(param->mem_root,
                                               param->fields_bitmap_size);
  if (!covered_fields->bitmap ||
      my_bitmap_init(covered_fields, covered_fields->bitmap,
                  param->table->s->fields))
    DBUG_RETURN(0);
  bitmap_clear_all(covered_fields);

  double total_cost= 0.0;
  ha_rows records=0;
  bool all_covered;

  DBUG_PRINT("info", ("Building covering ROR-intersection"));
  DBUG_EXECUTE("info", print_ror_scans_arr(param->table,
                                           "building covering ROR-I",
                                           ror_scan_mark, ror_scans_end););
  do
  {
    /*
      Update changed sorting info:
        #covered fields,
	number of first not covered component
      Calculate and save these values for each of remaining scans.
    */
    for (ROR_SCAN_INFO **scan= ror_scan_mark; scan != ror_scans_end; ++scan)
    {
      bitmap_subtract(&(*scan)->covered_fields, covered_fields);
      (*scan)->used_fields_covered=
        bitmap_bits_set(&(*scan)->covered_fields);
      (*scan)->first_uncovered_field=
        bitmap_get_first_clear(&(*scan)->covered_fields);
    }

    my_qsort(ror_scan_mark, ror_scans_end-ror_scan_mark, sizeof(ROR_SCAN_INFO*),
             cmp_ror_scan_info_covering);

    DBUG_EXECUTE("info", print_ror_scans_arr(param->table,
                                             "remaining scans",
                                             ror_scan_mark, ror_scans_end););

    /* I=I-first(I) */
    total_cost += (*ror_scan_mark)->index_read_cost;
    records += (*ror_scan_mark)->records;
    DBUG_PRINT("info", ("Adding scan on %s",
                        param->table->key_info[(*ror_scan_mark)->keynr].name.str));
    if (total_cost > read_time)
      DBUG_RETURN(NULL);
    /* F=F-covered by first(I) */
    bitmap_union(covered_fields, &(*ror_scan_mark)->covered_fields);
    all_covered= bitmap_is_subset(&param->needed_fields, covered_fields);
  } while ((++ror_scan_mark < ror_scans_end) && !all_covered);
  
  if (!all_covered || (ror_scan_mark - tree->ror_scans) == 1)
    DBUG_RETURN(NULL);

  /*
    Ok, [tree->ror_scans .. ror_scan) holds covering index_intersection with
    cost total_cost.
  */
  DBUG_PRINT("info", ("Covering ROR-intersect scans cost: %g", total_cost));
  DBUG_EXECUTE("info", print_ror_scans_arr(param->table,
                                           "creating covering ROR-intersect",
                                           tree->ror_scans, ror_scan_mark););

  /* Add priority queue use cost. */
  total_cost += (rows2double(records) *
                 log((double)(ror_scan_mark - tree->ror_scans)) *
                 ROWID_COMPARE_COST_THD(param->thd) / M_LN2);
  DBUG_PRINT("info", ("Covering ROR-intersect full cost: %g", total_cost));

  /* TODO: Add TIME_FOR_COMPARE cost to total_cost */

  if (total_cost > read_time)
    DBUG_RETURN(NULL);

  TRP_ROR_INTERSECT *trp;
  if (!(trp= new (param->mem_root) TRP_ROR_INTERSECT))
    DBUG_RETURN(trp);
  uint best_num= (uint)(ror_scan_mark - tree->ror_scans);
  if (!(trp->first_scan= (ROR_SCAN_INFO**)alloc_root(param->mem_root,
                                                     sizeof(ROR_SCAN_INFO*)*
                                                     best_num)))
    DBUG_RETURN(NULL);
  memcpy(trp->first_scan, tree->ror_scans, best_num*sizeof(ROR_SCAN_INFO*));
  trp->force_index_merge= force_index_merge;
  trp->last_scan=  trp->first_scan + best_num;
  trp->is_covering= TRUE;
  trp->read_cost= total_cost;
  trp->records= records;
  trp->cpk_scan= NULL;
  param->table->set_opt_range_condition_rows(records);

  DBUG_PRINT("exit",
             ("Returning covering ROR-intersect plan: cost %g, records %lu",
              trp->read_cost, (ulong) trp->records));
  DBUG_RETURN(trp);
}


/*
  Get best "range" table read plan for given SEL_TREE.
  Also update PARAM members and store ROR scans info in the SEL_TREE.
  SYNOPSIS
    get_key_scans_params
      param        parameters from test_quick_select
      tree         make range select for this SEL_TREE
      index_read_must_be_used if TRUE, assume 'index only' option will be set
                             (except for clustered PK indexes)
      for_range_access     if TRUE the function is called to get the best range
                           plan for range access, not for index merge access
      read_time    don't create read plans with cost > read_time.
  RETURN
    Best range read plan
    NULL if no plan found or error occurred
*/

static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
                                       bool index_read_must_be_used,
                                       bool for_range_access,
                                       double read_time, ha_rows limit,
                                       bool using_table_scan)
{
  uint idx, UNINIT_VAR(best_idx);
  SEL_ARG *key_to_read= NULL;
  ha_rows UNINIT_VAR(best_records);              /* protected by key_to_read */
  uint    UNINIT_VAR(best_mrr_flags),            /* protected by key_to_read */
          UNINIT_VAR(best_buf_size);             /* protected by key_to_read */
  TRP_RANGE* read_plan= NULL;
  DBUG_ENTER("get_key_scans_params");
  THD *thd= param->thd;
  /*
    Note that there may be trees that have type SEL_TREE::KEY but contain no
    key reads at all, e.g. tree for expression "key1 is not null" where key1
    is defined as "not null".
  */
  DBUG_EXECUTE("info", print_sel_tree(param, tree, &tree->keys_map,
                                      "tree scans"););
  Json_writer_array range_scan_alt(thd, "range_scan_alternatives");

  tree->ror_scans_map.clear_all();
  tree->n_ror_scans= 0;
  tree->index_scans= 0;
  if (!tree->keys_map.is_clear_all())
  {
    tree->index_scans=
      (INDEX_SCAN_INFO **) alloc_root(param->mem_root,
                                      sizeof(INDEX_SCAN_INFO *) * param->keys);
  }
  tree->index_scans_end= tree->index_scans;

  bool force_index_merge= false;
  bool use_cheapest_index_merge= false;
  for (idx= 0; idx < param->keys; idx++)
  {
    SEL_ARG *key= tree->keys[idx];
    if (!key)
      continue;

    ha_rows found_records;
    Cost_estimate cost;
    double found_read_time;
    uint mrr_flags, buf_size;
    bool is_ror_scan= FALSE;
    INDEX_SCAN_INFO *index_scan;
    uint keynr= param->real_keynr[idx];
    if (key->type == SEL_ARG::MAYBE_KEY ||
        key->maybe_flag)
      param->needed_reg->set_bit(keynr);

    bool read_index_only= index_read_must_be_used ? TRUE :
                          (bool) param->table->covering_keys.is_set(keynr);

    Json_writer_object trace_idx(thd);
    trace_idx.add("index", param->table->key_info[keynr].name);

    found_records= check_quick_select(param, idx, limit, read_index_only,
                                      key, for_range_access, &mrr_flags,
                                      &buf_size, &cost, &is_ror_scan);

    const index_merge_behavior ihb= index_merge_hint(param->table,  // do this before check_quick_select?
                                                     keynr,
                                                     &force_index_merge,
                                                     &use_cheapest_index_merge);
    if (ihb == index_merge_behavior::SKIP_KEY)
      continue;

    if (found_records == HA_POS_ERROR ||
        (!for_range_access && !is_ror_scan &&
         (!optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION) && !force_index_merge)))
    {
      /* The scan is not a ROR-scan, just skip it */
      continue;
    }
    found_read_time= cost.total_cost();
    if (tree->index_scans &&
        (index_scan= (INDEX_SCAN_INFO *)alloc_root(param->mem_root,
                                                   sizeof(INDEX_SCAN_INFO))))
    {
      Json_writer_array trace_range(thd, "ranges");
      const KEY &cur_key= param->table->key_info[keynr];
      const KEY_PART_INFO *key_part= cur_key.key_part;

      index_scan->idx= idx;
      index_scan->keynr= keynr;
      index_scan->key_info= &param->table->key_info[keynr];
      index_scan->used_key_parts= param->max_key_parts;
      index_scan->range_count= param->range_count;
      index_scan->records= found_records;
      index_scan->sel_arg= key;
      *tree->index_scans_end++= index_scan;

      if (unlikely(thd->trace_started()))
        trace_ranges(&trace_range, param, idx, key, key_part);
      trace_range.end();

      if (unlikely(trace_idx.trace_started()))
      {
        trace_idx.
          add("rowid_ordered", is_ror_scan).
          add("using_mrr", !(mrr_flags & HA_MRR_USE_DEFAULT_IMPL)).
          add("index_only", read_index_only).
          add("rows", found_records).
          add("cost", found_read_time);
        if (using_table_scan && cost.limit_cost != 0.0)
          trace_idx.add("cost_with_limit", cost.limit_cost);
      }
    }
    if (is_ror_scan)
    {
      tree->n_ror_scans++;
      tree->ror_scans_map.set_bit(idx);
    }
    /*
      Use range if best range so far or if we are comparing to a table scan
      and the cost with limit approximation is better than the table scan
    */
    if ((read_time > found_read_time ||
         (force_index_merge && (!use_cheapest_index_merge || !key_to_read))) ||
        (using_table_scan && cost.limit_cost != 0.0 &&
         read_time > cost.limit_cost))
    {
      read_time=    found_read_time;
      best_records= found_records;
      key_to_read=  key;
      best_idx= idx;
      best_mrr_flags= mrr_flags;
      best_buf_size=  buf_size;
      using_table_scan= 0;
      trace_idx.add("chosen", true);
    }
    else if (unlikely(trace_idx.trace_started()))
    {
      trace_idx.add("chosen", false);
      if (found_records == HA_POS_ERROR)
      {
        if (key->type == SEL_ARG::Type::MAYBE_KEY)
          trace_idx.add("cause", "depends on unread values");
        else
          trace_idx.add("cause", "unknown");
      }
      else
        trace_idx.add("cause", "cost");
    }
  }

  DBUG_EXECUTE("info", print_sel_tree(param, tree, &tree->ror_scans_map,
                                      "ROR scans"););
  if (key_to_read)
  {
    if ((read_plan= new (param->mem_root) TRP_RANGE(key_to_read, best_idx,
                                                    best_mrr_flags)))
    {
      read_plan->force_index_merge= force_index_merge;
      read_plan->records= best_records;
      read_plan->is_ror= tree->ror_scans_map.is_set(best_idx);
      read_plan->read_cost= read_time;
      read_plan->mrr_buf_size= best_buf_size;
      DBUG_PRINT("info",
                 ("Returning range plan for key %s, cost %g, records %lu",
                  param->table->key_info[param->real_keynr[best_idx]].name.str,
                  read_plan->read_cost, (ulong) read_plan->records));
    }
  }
  else
    DBUG_PRINT("info", ("No 'range' table read plan found"));

  DBUG_RETURN(read_plan);
}


QUICK_SELECT_I *TRP_INDEX_MERGE::make_quick(PARAM *param,
                                            bool retrieve_full_rows,
                                            MEM_ROOT *parent_alloc)
{
  QUICK_INDEX_MERGE_SELECT *quick_imerge;
  QUICK_RANGE_SELECT *quick;
  /* index_merge always retrieves full rows, ignore retrieve_full_rows */
  if (!(quick_imerge= new QUICK_INDEX_MERGE_SELECT(param->thd, param->table)))
    return NULL;

  quick_imerge->records= records;
  quick_imerge->read_time= read_cost;
  for (TRP_RANGE **range_scan= range_scans; range_scan != range_scans_end;
       range_scan++)
  {
    if (!(quick= (QUICK_RANGE_SELECT*)
          ((*range_scan)->make_quick(param, FALSE, &quick_imerge->alloc)))||
        quick_imerge->push_quick_back(quick))
    {
      delete quick;
      delete quick_imerge;
      return NULL;
    }
  }
  return quick_imerge;
}


QUICK_SELECT_I *TRP_INDEX_INTERSECT::make_quick(PARAM *param,
                                                bool retrieve_full_rows,
                                                MEM_ROOT *parent_alloc)
{
  QUICK_INDEX_INTERSECT_SELECT *quick_intersect;
  QUICK_RANGE_SELECT *quick;
  /* index_merge always retrieves full rows, ignore retrieve_full_rows */
  if (!(quick_intersect= new QUICK_INDEX_INTERSECT_SELECT(param->thd, param->table)))
    return NULL;

  quick_intersect->records= records;
  quick_intersect->read_time= read_cost;
  quick_intersect->filtered_scans= filtered_scans;
  for (TRP_RANGE **range_scan= range_scans; range_scan != range_scans_end;
       range_scan++)
  {
    if (!(quick= (QUICK_RANGE_SELECT*)
          ((*range_scan)->make_quick(param, FALSE, &quick_intersect->alloc)))||
        quick_intersect->push_quick_back(quick))
    {
      delete quick;
      delete quick_intersect;
      return NULL;
    }
  }
  return quick_intersect;
}


QUICK_SELECT_I *TRP_ROR_INTERSECT::make_quick(PARAM *param,
                                              bool retrieve_full_rows,
                                              MEM_ROOT *parent_alloc)
{
  QUICK_ROR_INTERSECT_SELECT *quick_intrsect;
  QUICK_RANGE_SELECT *quick;
  DBUG_ENTER("TRP_ROR_INTERSECT::make_quick");
  MEM_ROOT *alloc;

  if ((quick_intrsect=
         new QUICK_ROR_INTERSECT_SELECT(param->thd, param->table,
                                        (retrieve_full_rows? (!is_covering) :
                                         FALSE),
                                        parent_alloc)))
  {
    DBUG_EXECUTE("info", print_ror_scans_arr(param->table,
                                             "creating ROR-intersect",
                                             first_scan, last_scan););
    alloc= parent_alloc? parent_alloc: &quick_intrsect->alloc;
    for (ROR_SCAN_INFO **curr_scan= first_scan; curr_scan != last_scan;
                                                          ++curr_scan)
    {
      if (!(quick= get_quick_select(param, (*curr_scan)->idx,
                                    (*curr_scan)->sel_arg,
                                    HA_MRR_USE_DEFAULT_IMPL | HA_MRR_SORTED,
                                    0, alloc)) ||
          quick_intrsect->push_quick_back(alloc, quick))
      {
        delete quick_intrsect;
        DBUG_RETURN(NULL);
      }
    }
    if (cpk_scan)
    {
      if (!(quick= get_quick_select(param, cpk_scan->idx,
                                    cpk_scan->sel_arg,
                                    HA_MRR_USE_DEFAULT_IMPL | HA_MRR_SORTED,
                                    0, alloc)))
      {
        delete quick_intrsect;
        DBUG_RETURN(NULL);
      }
      quick->file= NULL; 
      quick_intrsect->cpk_quick= quick;
    }
    quick_intrsect->records= records;
    quick_intrsect->read_time= read_cost;
  }
  DBUG_RETURN(quick_intrsect);
}


QUICK_SELECT_I *TRP_ROR_UNION::make_quick(PARAM *param,
                                          bool retrieve_full_rows,
                                          MEM_ROOT *parent_alloc)
{
  QUICK_ROR_UNION_SELECT *quick_roru;
  TABLE_READ_PLAN **scan;
  QUICK_SELECT_I *quick;
  DBUG_ENTER("TRP_ROR_UNION::make_quick");
  /*
    It is impossible to construct a ROR-union that will not retrieve full
    rows, ignore retrieve_full_rows parameter.
  */
  if ((quick_roru= new QUICK_ROR_UNION_SELECT(param->thd, param->table)))
  {
    for (scan= first_ror; scan != last_ror; scan++)
    {
      if (!(quick= (*scan)->make_quick(param, FALSE, &quick_roru->alloc)) ||
          quick_roru->push_quick_back(quick))
      {
        delete quick_roru;
        DBUG_RETURN(NULL);
      }
    }
    quick_roru->records= records;
    quick_roru->read_time= read_cost;
  }
  DBUG_RETURN(quick_roru);
}


/*
  Build a SEL_TREE for <> or NOT BETWEEN predicate
 
  SYNOPSIS
    get_ne_mm_tree()
      param       PARAM from SQL_SELECT::test_quick_select
      cond_func   item for the predicate
      field       field in the predicate
      lt_value    constant that field should be smaller
      gt_value    constant that field should be greater

  RETURN 
    #  Pointer to tree built tree
    0  on error
*/

SEL_TREE *Item_bool_func::get_ne_mm_tree(RANGE_OPT_PARAM *param,
                                         Field *field,
                                         Item *lt_value, Item *gt_value)
{
  SEL_TREE *tree;
  tree= get_mm_parts(param, field, Item_func::LT_FUNC, lt_value);
  if (tree)
    tree= tree_or(param, tree, get_mm_parts(param, field, Item_func::GT_FUNC,
					    gt_value));
  return tree;
}


SEL_TREE *Item_func_ne::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                         Field *field, Item *value)
{
  DBUG_ENTER("Item_func_ne::get_func_mm_tree");
  /*
    If this condition is a "col1<>...", where there is a UNIQUE KEY(col1),
    do not construct a SEL_TREE from it. A condition that excludes just one
    row in the table is not selective (unless there are only a few rows)

    Note: this logic must be in sync with code in
    check_group_min_max_predicates(). That function walks an Item* condition
    and checks if the range optimizer would produce an equivalent range for
    it.
  */
  if (param->using_real_indexes && is_field_an_unique_index(field))
    DBUG_RETURN(NULL);
  DBUG_RETURN(get_ne_mm_tree(param, field, value, value));
}


SEL_TREE *Item_func_istrue::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                             Field *field, Item *value)
{
  DBUG_ENTER("Item_func_istrue::get_func_mm_tree");
  // See comments in Item_func_ne::get_func_mm_tree()
  if (param->using_real_indexes && is_field_an_unique_index(field))
    DBUG_RETURN(NULL);
  DBUG_RETURN(get_ne_mm_tree(param, field, value, value));
}


SEL_TREE *Item_func_isnotfalse::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                                 Field *field, Item *value)
{
  DBUG_ENTER("Item_func_notfalse::get_func_mm_tree");
  // See comments in Item_func_ne::get_func_mm_tree()
  if (param->using_real_indexes && is_field_an_unique_index(field))
    DBUG_RETURN(NULL);
  DBUG_RETURN(get_ne_mm_tree(param, field, value, value));
}


SEL_TREE *Item_func_isfalse::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                              Field *field,
                                              Item *value)
{
  DBUG_ENTER("Item_bool_isfalse::get_func_mm_tree");
  DBUG_RETURN(get_mm_parts(param, field, EQ_FUNC, value));
}


SEL_TREE *Item_func_isnottrue::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                                Field *field,
                                                Item *value)
{
  DBUG_ENTER("Item_func_isnottrue::get_func_mm_tree");
  DBUG_RETURN(get_mm_parts(param, field, EQ_FUNC, value));
}


SEL_TREE *Item_func_between::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                              Field *field, Item *value)
{
  SEL_TREE *tree;
  DBUG_ENTER("Item_func_between::get_func_mm_tree");
  if (!value)
  {
    if (negated)
    {
      tree= get_ne_mm_tree(param, field, args[1], args[2]);
    }
    else
    {
      tree= get_mm_parts(param, field, Item_func::GE_FUNC, args[1]);
      if (tree)
      {
        tree= tree_and(param, tree, get_mm_parts(param, field,
                                                 Item_func::LE_FUNC,
                                                 args[2]));
      }
    }
  }
  else
  {
    tree= get_mm_parts(param, field,
                       (negated ?
                        (value == (Item*)1 ? Item_func::GT_FUNC :
                                             Item_func::LT_FUNC):
                        (value == (Item*)1 ? Item_func::LE_FUNC :
                                             Item_func::GE_FUNC)),
                       args[0]);
  }
  DBUG_RETURN(tree);
}


SEL_TREE *Item_func_in::get_func_mm_tree(RANGE_OPT_PARAM *param,
                                         Field *field, Item *value)
{
  SEL_TREE *tree= 0;
  DBUG_ENTER("Item_func_in::get_func_mm_tree");
  /*
    Array for IN() is constructed when all values have the same result
    type. Tree won't be built for values with different result types,
    so we check it here to avoid unnecessary work.
  */
  if (!arg_types_compatible)
    DBUG_RETURN(0);

  if (negated)
  {
    if (array && array->type_handler()->result_type() != ROW_RESULT)
    {
      /*
        We get here for conditions in form "t.key NOT IN (c1, c2, ...)",
        where c{i} are constants. Our goal is to produce a SEL_TREE that
        represents intervals:

        ($MIN<t.key<c1) OR (c1<t.key<c2) OR (c2<t.key<c3) OR ...    (*)

        where $MIN is either "-inf" or NULL.

        The most straightforward way to produce it is to convert NOT IN
        into "(t.key != c1) AND (t.key != c2) AND ... " and let the range
        analyzer to build SEL_TREE from that. The problem is that the
        range analyzer will use O(N^2) memory (which is probably a bug),
        and people do use big NOT IN lists (e.g. see BUG#15872, BUG#21282),
        will run out of memory.

        Another problem with big lists like (*) is that a big list is
        unlikely to produce a good "range" access, while considering that
        range access will require expensive CPU calculations (and for
        MyISAM even index accesses). In short, big NOT IN lists are rarely
        worth analyzing.

        Considering the above, we'll handle NOT IN as follows:
        * if the number of entries in the NOT IN list is less than
          NOT_IN_IGNORE_THRESHOLD, construct the SEL_TREE (*) manually.
        * Otherwise, don't produce a SEL_TREE.
      */
#define NOT_IN_IGNORE_THRESHOLD 1000
      MEM_ROOT *tmp_root= param->mem_root;
      param->thd->mem_root= param->old_root;
      /* 
        Create one Item_type constant object. We'll need it as
        get_mm_parts only accepts constant values wrapped in Item_Type
        objects.
        We create the Item on param->mem_root which points to
        per-statement mem_root (while thd->mem_root is currently pointing
        to mem_root local to range optimizer).
      */
      Item *value_item= array->create_item(param->thd);
      param->thd->mem_root= tmp_root;

      if (array->count > NOT_IN_IGNORE_THRESHOLD || !value_item)
        DBUG_RETURN(0);

      /*
        if this is a "col1 NOT IN (...)", and there is a UNIQUE KEY(col1), do
        not construct a SEL_TREE from it. The rationale is as follows:
         - if there are only a few constants, this condition is not selective
           (unless the table is also very small in which case we won't gain
           anything)
         - if there are a lot of constants, the overhead of building and
           processing enormous range list is not worth it.
      */
      if (param->using_real_indexes && is_field_an_unique_index(field))
        DBUG_RETURN(0);

      /* Get a SEL_TREE for "(-inf|NULL) < X < c_0" interval.  */
      uint i=0;
      do
      {
        array->value_to_item(i, value_item);
        tree= get_mm_parts(param, field, Item_func::LT_FUNC, value_item);
        if (!tree)
          break;
        i++;
      } while (i < array->used_count && tree->type == SEL_TREE::IMPOSSIBLE);

      if (!tree || tree->type == SEL_TREE::IMPOSSIBLE)
      {
        /* We get here in cases like "t.unsigned NOT IN (-1,-2,-3) */
        DBUG_RETURN(NULL);
      }
      SEL_TREE *tree2;
      for (; i < array->used_count; i++)
      {
        if (array->compare_elems(i, i-1))
        {
          /* Get a SEL_TREE for "-inf < X < c_i" interval */
          array->value_to_item(i, value_item);
          tree2= get_mm_parts(param, field, Item_func::LT_FUNC, value_item);
          if (!tree2)
          {
            tree= NULL;
            break;
          }

          /* Change all intervals to be "c_{i-1} < X < c_i" */
          for (uint idx= 0; idx < param->keys; idx++)
          {
            SEL_ARG *new_interval, *last_val;
            if (((new_interval= tree2->keys[idx])) &&
                (tree->keys[idx]) &&
                ((last_val= tree->keys[idx]->last())))
            {
              new_interval->min_value= last_val->max_value;
              new_interval->min_flag= NEAR_MIN;

              /*
                If the interval is over a partial keypart, the
                interval must be "c_{i-1} <= X < c_i" instead of
                "c_{i-1} < X < c_i". Reason:

                Consider a table with a column "my_col VARCHAR(3)",
                and an index with definition
                "INDEX my_idx my_col(1)". If the table contains rows
                with my_col values "f" and "foo", the index will not
                distinguish the two rows.

                Note that tree_or() below will effectively merge
                this range with the range created for c_{i-1} and
                we'll eventually end up with only one range:
                "NULL < X".

                Partitioning indexes are never partial.
              */
              if (param->using_real_indexes)
              {
                const KEY key=
                  param->table->key_info[param->real_keynr[idx]];
                const KEY_PART_INFO *kpi= key.key_part + new_interval->part;

                if (kpi->key_part_flag & HA_PART_KEY_SEG)
                  new_interval->min_flag= 0;
              }
            }
          }
          /* 
            The following doesn't try to allocate memory so no need to
            check for NULL.
          */
          tree= tree_or(param, tree, tree2);
        }
      }

      if (tree && tree->type != SEL_TREE::IMPOSSIBLE)
      {
        /*
          Get the SEL_TREE for the last "c_last < X < +inf" interval
          (value_item contains c_last already)
        */
        tree2= get_mm_parts(param, field, Item_func::GT_FUNC, value_item);
        tree= tree_or(param, tree, tree2);
      }
    }
    else
    {
      tree= get_ne_mm_tree(param, field, args[1], args[1]);
      if (tree)
      {
        Item **arg, **end;
        for (arg= args + 2, end= arg + arg_count - 2; arg < end ; arg++)
        {
          tree=  tree_and(param, tree, get_ne_mm_tree(param, field,
                                                      *arg, *arg));
        }
      }
    }
  }
  else
  {
    tree= get_mm_parts(param, field, Item_func::EQ_FUNC, args[1]);
    if (tree)
    {
      Item **arg, **end;
      for (arg= args + 2, end= arg + arg_count - 2;
           arg < end ; arg++)
      {
        tree= tree_or(param, tree, get_mm_parts(param, field,
                                                Item_func::EQ_FUNC, *arg));
      }
    }
  }
  DBUG_RETURN(tree);
}


/*
  The structure Key_col_info is purely  auxiliary and is used
  only in the method Item_func_in::get_func_row_mm_tree
*/ 
struct Key_col_info {
  Field *field;         /* If != NULL the column can be used for keys */
  cmp_item *comparator; /* If != 0 the column can be evaluated        */
};

/**
    Build SEL_TREE for the IN predicate whose arguments are rows 

    @param param          PARAM from SQL_SELECT::test_quick_select
    @param key_row        First operand of the IN predicate

  @note
    The function builds a SEL_TREE for in IN predicate in the case
    when the predicate uses row arguments. First the function
    detects among the components of the key_row (c[1],...,c[n]) taken 
    from in the left part the predicate those that can be usable
    for building SEL_TREE (c[i1],...,c[ik]).  They have to contain
    items whose real items are  field items referring to the current
    table or equal to the items referring to the current table.
    For the remaining components of the row it checks whether they
    can be evaluated. The result of the analysis is put into the
    array of structures of the type Key_row_col_info.

    After this the function builds the SEL_TREE for the following 
    formula that can be inferred from the given IN predicate:
      c[i11]=a[1][i11] AND ... AND c[i1k1]=a[1][i1k1]
      OR   
      ...
      OR
      c[im1]=a[m][im1] AND ... AND c[imkm]=a[m][imkm].
    Here a[1],...,a[m] are all arguments of the IN predicate from
    the right part and for each j ij1,...,ijkj is a subset of
    i1,...,ik such that a[j][ij1],...,a[j][ijkj] can be evaluated.

    If for some j there no a[j][i1],...,a[j][ik] can be evaluated
    then no SEL_TREE can be built for this predicate and the
    function immediately returns 0.

    If for some j by using evaluated values of key_row it can be
    proven that c[ij1]=a[j][ij1] AND ... AND c[ijkj]=a[j][ijkj]
    is always FALSE then this disjunct is omitted. 

  @returns
    the built SEL_TREE if it can be constructed
    0 - otherwise.
*/

SEL_TREE *Item_func_in::get_func_row_mm_tree(RANGE_OPT_PARAM *param,
                                             Item_row *key_row)
{
  DBUG_ENTER("Item_func_in::get_func_row_mm_tree");

  if (negated)
    DBUG_RETURN(0);

  SEL_TREE *res_tree= 0;
  uint used_key_cols= 0;
  uint col_comparators= 0;
  table_map param_comp= ~(param->prev_tables | param->read_tables |
                          param->current_table);
  uint row_cols= key_row->cols();
  Dynamic_array <Key_col_info> key_cols_info(PSI_INSTRUMENT_MEM,row_cols);
  cmp_item_row *row_cmp_item;

  if (array)
  {
    in_row *row= static_cast<in_row*>(array);
    row_cmp_item= static_cast<cmp_item_row*>(row->get_cmp_item());
  }
  else
  {
    DBUG_ASSERT(get_comparator_type_handler(0) == &type_handler_row);
    row_cmp_item= static_cast<cmp_item_row*>(get_comparator_cmp_item(0));
  }
  DBUG_ASSERT(row_cmp_item);

  Item **key_col_ptr= key_row->addr(0);
  for(uint i= 0; i < row_cols;  i++, key_col_ptr++)
  {
    Key_col_info key_col_info= {0, NULL};
    Item *key_col= *key_col_ptr;
    if (key_col->real_item()->type() == Item::FIELD_ITEM)
    {
      /*
        The i-th component of key_row can be used for key access if 
        key_col->real_item() points to a field of the current table or
        if it is equal to a field item pointing to such a field.
      */
      Item_field *col_field_item= (Item_field *) (key_col->real_item());
      Field *key_col_field= col_field_item->field;
      if (key_col_field->table->map != param->current_table)
      {
        Item_equal *item_equal= col_field_item->item_equal;
        if (item_equal)
        {
          Item_equal_fields_iterator it(*item_equal);
          while (it++)
	  {
            key_col_field= it.get_curr_field();
            if (key_col_field->table->map == param->current_table)
              break;
          }
        }
      }
      if (key_col_field->table->map == param->current_table)
      {
        key_col_info.field= key_col_field;
        used_key_cols++;
      }
    }
    else if (!(key_col->used_tables() & (param_comp | param->current_table))
             && !key_col->is_expensive())
    {
      /* The i-th component of key_row can be evaluated */

      /* See the comment in Item::get_mm_tree_for_const */
      MEM_ROOT *tmp_root= param->mem_root;
      param->thd->mem_root= param->old_root;

      key_col->bring_value();
      key_col_info.comparator= row_cmp_item->get_comparator(i);
      DBUG_ASSERT(key_col_info.comparator);
      key_col_info.comparator->store_value(key_col);
      col_comparators++;

      param->thd->mem_root= tmp_root;
    }
    key_cols_info.push(key_col_info);
  }

  if (!used_key_cols)
    DBUG_RETURN(0);

  uint omitted_tuples= 0;
  Item **arg_start= arguments() + 1;
  Item **arg_end= arg_start + argument_count() - 1;
  for (Item **arg= arg_start ; arg < arg_end; arg++)
  {
    uint i;
   
    /* 
      First check whether the disjunct constructed for *arg
      is really needed
    */  
    Item_row *arg_tuple= (Item_row *) (*arg);
    if (col_comparators)
    {
      MEM_ROOT *tmp_root= param->mem_root;
      param->thd->mem_root= param->old_root;
      for (i= 0; i < row_cols; i++)
      {
        Key_col_info *key_col_info= &key_cols_info.at(i);
        if (key_col_info->comparator)
	{
          Item *arg_col= arg_tuple->element_index(i);
          if (!(arg_col->used_tables() & (param_comp | param->current_table)) &&
	      !arg_col->is_expensive() &&
              key_col_info->comparator->cmp(arg_col))
	  {
            omitted_tuples++;
            break;
          }
        }
      }
      param->thd->mem_root= tmp_root;
      if (i < row_cols)
        continue;
    }
    
    /* The disjunct for *arg is needed: build it. */     
    SEL_TREE *and_tree= 0;
    Item **arg_col_ptr= arg_tuple->addr(0);
    for (uint i= 0; i < row_cols; i++, arg_col_ptr++)
    { 
      Key_col_info *key_col_info= &key_cols_info.at(i);
      if (!key_col_info->field)
        continue;
      Item *arg_col= *arg_col_ptr;
      if (!(arg_col->used_tables() & (param_comp | param->current_table)) &&
	  !arg_col->is_expensive())
      {
        and_tree= tree_and(param, and_tree, 
                           get_mm_parts(param,
                                        key_col_info->field, 
                                        Item_func::EQ_FUNC,
                                        arg_col->real_item()));
      }
    }
    if (!and_tree)
    {
      res_tree= 0;
      break;
    }
    /* Join the disjunct the OR tree that is being constructed */
    res_tree= !res_tree ? and_tree : tree_or(param, res_tree, and_tree);
  }
  if (omitted_tuples == argument_count() - 1)
  {
    /* It's turned out that all disjuncts are always FALSE */
    res_tree= new (param->mem_root) SEL_TREE(SEL_TREE::IMPOSSIBLE,
                                             param->mem_root, param->keys);
  }
  DBUG_RETURN(res_tree);
}


/*
  Build conjunction of all SEL_TREEs for a simple predicate applying equalities

  SYNOPSIS
    get_full_func_mm_tree()
      param       PARAM from SQL_SELECT::test_quick_select
      field_item  field in the predicate
      value       constant in the predicate (or a field already read from
                  a table in the case of dynamic range access)
                  (for BETWEEN it contains the number of the field argument,
                   for IN it's always 0)
      inv         TRUE <> NOT cond_func is considered
                  (makes sense only when cond_func is BETWEEN or IN)

  DESCRIPTION
    For a simple SARGable predicate of the form (f op c), where f is a field
    and c is a constant, the function builds a conjunction of all SEL_TREES that
    can be obtained by the substitution of f for all different fields equal to f.

  NOTES
    If the WHERE condition contains a predicate (fi op c),
    then not only SELL_TREE for this predicate is built, but
    the trees for the results of substitution of fi for
    each fj belonging to the same multiple equality as fi
    are built as well.
    E.g. for WHERE t1.a=t2.a AND t2.a > 10
    a SEL_TREE for t2.a > 10 will be built for quick select from t2
    and
    a SEL_TREE for t1.a > 10 will be built for quick select from t1.

    A BETWEEN predicate of the form (fi [NOT] BETWEEN c1 AND c2), where fi
    is some field, is treated in a similar way: we build a conjuction of
    trees for the results of all substitutions of fi equal fj.

    Yet a predicate of the form (c BETWEEN f1i AND f2i) is processed
    differently. It is considered as a conjuction of two SARGable
    predicates (f1i <= c) and (c <= f2i) and the function get_full_func_mm_tree
    is called for each of them separately producing trees for
       AND j (f1j <= c) and AND j (c <= f2j)
    After this these two trees are united in one conjunctive tree.
    It's easy to see that the same tree is obtained for
       AND j,k (f1j <= c AND c <= f2k)
    which is equivalent to
       AND j,k (c BETWEEN f1j AND f2k).

    The validity of the processing of the predicate (c NOT BETWEEN f1i AND f2i)
    which equivalent to (f1i > c OR f2i < c) is not so obvious. Here the
    function get_full_func_mm_tree is called for (f1i > c) and called for
    (f2i < c) producing trees for AND j (f1j > c) and AND j (f2j < c). Then
    this two trees are united in one OR-tree. The expression
      (AND j (f1j > c) OR AND j (f2j < c)
    is equivalent to the expression
      AND j,k (f1j > c OR f2k < c)
    which is just a translation of
      AND j,k (c NOT BETWEEN f1j AND f2k)

    In the cases when one of the items f1, f2 is a constant c1 we do not create
    a tree for it at all. It works for BETWEEN predicates but does not
    work for NOT BETWEEN predicates as we have to evaluate the expression
    with it. If it is TRUE then the other tree can be completely ignored.
    We do not do it now and no trees are built in these cases for
    NOT BETWEEN predicates.

    As to IN predicates only ones of the form (f IN (c1,...,cn)),
    where f1 is a field and c1,...,cn are constant, are considered as
    SARGable. We never try to narrow the index scan using predicates of
    the form (c IN (c1,...,f,...,cn)).

  RETURN
    Pointer to the tree representing the built conjunction of SEL_TREEs
*/

SEL_TREE *Item_bool_func::get_full_func_mm_tree(RANGE_OPT_PARAM *param,
                                                Item_field *field_item,
                                                Item *value)
{
  DBUG_ENTER("Item_bool_func::get_full_func_mm_tree");
  SEL_TREE *tree= 0;
  SEL_TREE *ftree= 0;
  table_map ref_tables= 0;
  table_map param_comp= ~(param->prev_tables | param->read_tables |
		          param->current_table);

  for (uint i= 0; i < arg_count; i++)
  {
    Item *arg= arguments()[i]->real_item();
    if (arg != field_item)
      ref_tables|= arg->used_tables();
  }
  Field *field= field_item->field;
  if (!((ref_tables | field->table->map) & param_comp))
    ftree= get_func_mm_tree(param, field, value);
  Item_equal *item_equal= field_item->item_equal;
  if (item_equal)
  {
    Item_equal_fields_iterator it(*item_equal);
    while (it++)
    {
      Field *f= it.get_curr_field();
      if (field->eq(f))
        continue;
      if (!((ref_tables | f->table->map) & param_comp))
      {
        tree= get_func_mm_tree(param, f, value);
        ftree= !ftree ? tree : tree_and(param, ftree, tree);
      }
    }
  }

  DBUG_RETURN(ftree);
}


/* 
  make a select tree of all keys in condition 
  
  @param  param  Context
  @param  cond  INOUT condition to perform range analysis on.

  @detail
    Range analysis may infer that some conditions are never true. 
    - If the condition is never true, SEL_TREE(type=IMPOSSIBLE) is returned
    - if parts of condition are never true, the function may remove these parts
      from the condition 'cond'.  Sometimes, this will cause the condition to
      be substituted for something else.


  @return 
    NULL     - Could not infer anything from condition cond.
    SEL_TREE with type=IMPOSSIBLE - condition can never be true.
*/
SEL_TREE *Item_cond_and::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_cond_and::get_mm_tree");
  SEL_TREE *tree= NULL;
  List_iterator<Item> li(*argument_list());
  Item *item;
  while ((item= li++))
  {
    SEL_TREE *new_tree= li.ref()[0]->get_mm_tree(param,li.ref());
    if (param->statement_should_be_aborted())
      DBUG_RETURN(NULL);
    tree= tree_and(param, tree, new_tree);
    if (tree && tree->type == SEL_TREE::IMPOSSIBLE)
    {
      /*
        Do not remove 'item' from 'cond'. We return a SEL_TREE::IMPOSSIBLE
        and that is sufficient for the caller to see that the whole
        condition is never true.
      */
      break;
    }
  }
  DBUG_RETURN(tree);
}


SEL_TREE *Item_cond::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_cond::get_mm_tree");
  List_iterator<Item> li(*argument_list());
  bool replace_cond= false;
  Item *replacement_item= li++;
  SEL_TREE *tree= li.ref()[0]->get_mm_tree(param, li.ref());
  if (param->statement_should_be_aborted())
    DBUG_RETURN(NULL);
  bool orig_disable_index_merge= param->disable_index_merge_plans;

  if (list.elements > MAX_OR_ELEMENTS_FOR_INDEX_MERGE)
    param->disable_index_merge_plans= true;

  if (tree)
  {
    if (tree->type == SEL_TREE::IMPOSSIBLE &&
        param->remove_false_where_parts)
    {
      /* See the other li.remove() call below */
      li.remove();
      if (argument_list()->elements <= 1)
        replace_cond= true;
    }

    Item *item;
    while ((item= li++))
    {
      SEL_TREE *new_tree= li.ref()[0]->get_mm_tree(param, li.ref());
      if (new_tree == NULL || param->statement_should_be_aborted())
      {
        param->disable_index_merge_plans= orig_disable_index_merge;
        DBUG_RETURN(NULL);
      }
      tree= tree_or(param, tree, new_tree);
      if (tree == NULL || tree->type == SEL_TREE::ALWAYS)
      {
        replacement_item= *li.ref();
        break;
      }

      if (new_tree && new_tree->type == SEL_TREE::IMPOSSIBLE &&
          param->remove_false_where_parts)
      {
        /*
          This is a condition in form

            cond = item1 OR ... OR item_i OR ... itemN

          and item_i produces SEL_TREE(IMPOSSIBLE). We should remove item_i
          from cond.  This may cause 'cond' to become a degenerate,
          one-way OR. In that case, we replace 'cond' with the remaining
          item_i.
        */
        li.remove();
        if (argument_list()->elements <= 1)
          replace_cond= true;
      }
      else
        replacement_item= *li.ref();
    }

    if (replace_cond)
      *cond_ptr= replacement_item;
  }
  param->disable_index_merge_plans= orig_disable_index_merge;
  DBUG_RETURN(tree);
}


SEL_TREE *Item::get_mm_tree_for_const(RANGE_OPT_PARAM *param)
{
  DBUG_ENTER("get_mm_tree_for_const");
  if (is_expensive())
    DBUG_RETURN(0);
  /*
    During the cond->val_int() evaluation we can come across a subselect
    item which may allocate memory on the thd->mem_root and assumes
    all the memory allocated has the same life span as the subselect
    item itself. So we have to restore the thread's mem_root here.
  */
  MEM_ROOT *tmp_root= param->mem_root;
  param->thd->mem_root= param->old_root;
  SEL_TREE *tree;

  const SEL_TREE::Type type= val_bool()? SEL_TREE::ALWAYS: SEL_TREE::IMPOSSIBLE;
  param->thd->mem_root= tmp_root;

  tree= new (tmp_root) SEL_TREE(type, tmp_root, param->keys);
  DBUG_RETURN(tree);
}


SEL_TREE *Item::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item::get_mm_tree");
  if (const_item())
    DBUG_RETURN(get_mm_tree_for_const(param));

  /*
    Here we have a not-constant non-function Item.

    Item_field should not appear, as normalize_cond() replaces
    "WHERE field" to "WHERE field<>0".

    Item_exists_subselect is possible, e.g. in this query:
    SELECT id, st FROM t1
    WHERE st IN ('GA','FL') AND EXISTS (SELECT 1 FROM t2 WHERE t2.id=t1.id)
    GROUP BY id;
  */
  table_map ref_tables= used_tables();
  if ((ref_tables & param->current_table) ||
      (ref_tables & ~(param->prev_tables | param->read_tables)))
    DBUG_RETURN(0);
  DBUG_RETURN(new (param->mem_root) SEL_TREE(SEL_TREE::MAYBE, param->mem_root, 
                                             param->keys));
}


bool
Item_func_between::can_optimize_range_const(Item_field *field_item) const
{
  const Type_handler *fi_handler= field_item->type_handler_for_comparison();
  Type_handler_hybrid_field_type cmp(fi_handler);
  if (cmp.aggregate_for_comparison(args[0]->type_handler_for_comparison()) ||
      cmp.type_handler() != m_comparator.type_handler())
      return false;  // Cannot optimize range because of type mismatch.

  return true;
}


SEL_TREE *
Item_func_between::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_func_between::get_mm_tree");
  if (const_item())
    DBUG_RETURN(get_mm_tree_for_const(param));

  SEL_TREE *tree= 0;
  SEL_TREE *ftree= 0;

  if (arguments()[0]->real_item()->type() == Item::FIELD_ITEM)
  {
    Item_field *field_item= (Item_field*) (arguments()[0]->real_item());
    ftree= get_full_func_mm_tree(param, field_item, NULL);
  }

  /*
    Concerning the code below see the NOTES section in
    the comments for the function get_full_func_mm_tree()
  */
  for (uint i= 1 ; i < arg_count ; i++)
  {
    if (arguments()[i]->real_item()->type() == Item::FIELD_ITEM)
    {
      Item_field *field_item= (Item_field*) (arguments()[i]->real_item());
      if (!can_optimize_range_const(field_item))
        continue;
      SEL_TREE *tmp= get_full_func_mm_tree(param, field_item,
                                           (Item*)(intptr) i);
      if (negated)
      {
        tree= !tree ? tmp : tree_or(param, tree, tmp);
        if (tree == NULL)
          break;
      }
      else
        tree= tree_and(param, tree, tmp);
    }
    else if (negated)
    {
      tree= 0;
      break;
    }
  }

  ftree= tree_and(param, ftree, tree);
  DBUG_RETURN(ftree);
}


SEL_TREE *Item_func_in::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_func_in::get_mm_tree");
  if (const_item())
    DBUG_RETURN(get_mm_tree_for_const(param));

  SEL_TREE *tree= 0;
  switch (key_item()->real_item()->type()) {
  case Item::FIELD_ITEM:
    tree= get_full_func_mm_tree(param,
                                (Item_field*) (key_item()->real_item()),
                                NULL);
    break;
  case Item::ROW_ITEM:
    tree= get_func_row_mm_tree(param,
			       (Item_row *) (key_item()->real_item()));
    break;
  default:
    DBUG_RETURN(0);
  } 
  DBUG_RETURN(tree);
} 


SEL_TREE *Item_func_truth::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_func_truth::get_mm_tree");
  DBUG_ASSERT(arg_count == 1);
  MEM_ROOT *old_root= param->thd->mem_root;
  param->thd->mem_root= param->old_root;
  Item *tmp= args[0]->type_handler()->create_boolean_false_item(param->thd);
  param->thd->mem_root= old_root;

  SEL_TREE *ftree= get_full_func_mm_tree_for_args(param, args[0], tmp);
  if (!ftree)
    goto err;
  if (!affirmative) // x IS NOT {TRUE|FALSE}
  {
    /*
      A non-affirmative boolean test works as follows:
        - NULL IS NOT FALSE returns TRUE
        - NULL IS NOT TRUE  returns TRUE
      Let's add the "x IS NULL" tree:
    */
    SEL_TREE *ftree2= get_full_func_mm_tree_for_args(param, args[0], NULL);
    if (!ftree2)
      goto err;
    ftree= tree_or(param, ftree, ftree2);
  }
err:
  if (!ftree)
    ftree= Item_func::get_mm_tree(param, cond_ptr);
  DBUG_RETURN(ftree);
}


SEL_TREE *Item_equal::get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
{
  DBUG_ENTER("Item_equal::get_mm_tree");
  if (const_item())
    DBUG_RETURN(get_mm_tree_for_const(param));

  SEL_TREE *tree= 0;
  SEL_TREE *ftree= 0;

  Item *value;
  if (!(value= get_const()) || value->is_expensive())
    DBUG_RETURN(0);

  Item_equal_fields_iterator it(*this);
  table_map ref_tables= value->used_tables();
  table_map param_comp= ~(param->prev_tables | param->read_tables |
		          param->current_table);
  while (it++)
  {
    Field *field= it.get_curr_field();
    if (!((ref_tables | field->table->map) & param_comp))
    {
      tree= get_mm_parts(param, field, Item_func::EQ_FUNC, value);
      ftree= !ftree ? tree : tree_and(param, ftree, tree);
    }
  }

  DBUG_RETURN(ftree);
}


/*
  @brief
    Check if there is an one-segment unique key that matches the field exactly

  @detail
    In the future we could also add "almost unique" indexes where any value is
    present only in a few rows (but necessarily exactly one row)
*/
static bool is_field_an_unique_index(Field *field)
{
  DBUG_ENTER("is_field_an_unique_index");
  key_map::Iterator it(field->key_start);
  uint key_no;
  while ((key_no= it++) != key_map::Iterator::BITMAP_END)
  {
    KEY *key_info= &field->table->key_info[key_no];
    if (key_info->user_defined_key_parts == 1 &&
        (key_info->flags & HA_NOSAME))
    {
      DBUG_RETURN(true);
    }
  }
  DBUG_RETURN(false);
}


/*
  @brief
    Given a string, escape the LIKE pattern characters (%, _, \) with the '\'.

  @detail
    Currently we fail if the escaped string didn't fit into MAX_FIELD_WIDTH
    bytes but this is not necessary.
*/

static bool escape_like_characters(String *res)
{
  CHARSET_INFO *cs= res->charset();
  StringBuffer<MAX_FIELD_WIDTH> tmp2(cs);
  tmp2.copy(*res);
  int ret;
  uchar *src= (uchar *) tmp2.ptr(), *src_end= (uchar *) tmp2.end(),
    *dst= (uchar *) res->ptr(), *dst_end= dst + MAX_FIELD_WIDTH;
  my_wc_t wc;
  while (src < src_end)
  {
    /* Advance to the next character */
    if ((ret= my_ci_mb_wc(cs, &wc, src, src_end)) <= 0)
    {
      if (ret == MY_CS_ILSEQ) /* Bad sequence */
        return true;       /* Cannot LIKE optimize */
      break;                  /* End of the string */
    }
    src+= ret;

    /* If the next char is escape-able in actual LIKE, escape it */
    if (wc == (my_wc_t) '%' || wc == (my_wc_t) '_' || wc == (my_wc_t) '\\')
    {
      if ((ret= my_ci_wc_mb(cs, (my_wc_t) '\\', dst, dst_end)) <= 0)
        return true; /* No space - no LIKE optimize */
      dst+= ret;
    }
    if ((ret= my_ci_wc_mb(cs, wc, dst, dst_end)) <= 0)
      return true; /* No space - no LIKE optimize */
    dst+= ret;
  }
  res->length((char *) dst - res->ptr());
  return false; /* Ok */
}


/*
  @brief
    Produce SEL_ARG interval for LIKE and prefix match functions.

  @detail
    This is used for conditions in forms:

     - key_col LIKE 'sargable_pattern'
     - SUBSTR(key_col, 1, ...) = 'value', or equivalent conditions involving
       LEFT() instead of SUBSTR() - see with_sargable_substr() for details.

  @param
     item The comparison item (Item_func_like or Item_func_eq)
*/

static SEL_ARG *
get_mm_leaf_for_LIKE(Item_bool_func *item, RANGE_OPT_PARAM *param,
                     Field *field, KEY_PART *key_part,
                     Item_func::Functype type, Item *value)
{
  DBUG_ENTER("get_mm_leaf_for_sargable");
  DBUG_ASSERT(value);

  if (key_part->image_type != Field::itRAW)
    DBUG_RETURN(0);

  uint keynr= param->real_keynr[key_part->key];
  if (param->using_real_indexes &&
      !field->optimize_range(keynr, key_part->part))
    DBUG_RETURN(0);

  if (field->result_type() == STRING_RESULT &&
      field->charset() != item->compare_collation())
  {
    /*
      For equalities where one side is LEFT or SUBSTR
      param->note_unusable_keys is BITMAP_EXCEPT_ANY_EQUALITY and the
      following if condition is satisfied. But it will not result in
      duplicate warnings because the ref optimizer does not cover this
      case.
    */
    if (param->note_unusable_keys & Item_func::BITMAP_LIKE)
      field->raise_note_cannot_use_key_part(param->thd, keynr, key_part->part,
                                            item->func_name_cstring(),
                                            item->compare_collation(),
                                            value,
                                            Data_type_compatibility::
                                            INCOMPATIBLE_COLLATION);
    DBUG_RETURN(0);
  }

  StringBuffer<MAX_FIELD_WIDTH> tmp(value->collation.collation);
  String *res;

  if (!(res= value->val_str(&tmp)))
    DBUG_RETURN(&null_element);

  if (field->cmp_type() != STRING_RESULT ||
      field->type_handler() == &type_handler_enum ||
      field->type_handler() == &type_handler_set)
  {
    if (param->note_unusable_keys & Item_func::BITMAP_LIKE)
      field->raise_note_cannot_use_key_part(param->thd, keynr, key_part->part,
                                            item->func_name_cstring(),
                                            item->compare_collation(),
                                            value,
                                            Data_type_compatibility::
                                            INCOMPATIBLE_DATA_TYPE);
    DBUG_RETURN(0);
  }

  /*
    TODO:
    Check if this was a function. This should have be optimized away
    in the sql_select.cc
  */
  if (res != &tmp)
  {
    tmp.copy(*res);				// Get own copy
    res= &tmp;
  }

  /*
    If we're handling a predicate in one of these forms:
     - LEFT(key_col, N) ='string_const'
     - SUBSTRING(key_col, 1, N)='string_const'

    then we need to:
    - escape the LIKE pattern characters in the string_const,
    - make the search pattern to be 'string_const%':
  */
  if (type != Item_func::LIKE_FUNC)
  {
    DBUG_ASSERT(type == Item_func::EQ_FUNC);
    if (escape_like_characters(res))
      DBUG_RETURN(0); /* Error, no optimization */
    res->append("%", 1);
  }

  uint maybe_null= (uint) field->real_maybe_null();
  size_t field_length= field->pack_length() + maybe_null;
  size_t offset= maybe_null;
  size_t length= key_part->store_length;

  if (length != key_part->length + maybe_null)
  {
    /* key packed with length prefix */
    offset+= HA_KEY_BLOB_LENGTH;
    field_length= length - HA_KEY_BLOB_LENGTH;
  }
  else
  {
    if (unlikely(length < field_length))
    {
      /*
        This can only happen in a table created with UNIREG where one key
        overlaps many fields
      */
      length= field_length;
    }
    else
      field_length= length;
  }
  length+= offset;
  uchar *min_str,*max_str;
  if (!(min_str= (uchar*) alloc_root(param->mem_root, length*2)))
    DBUG_RETURN(0);
  max_str= min_str + length;
  if (maybe_null)
    max_str[0]= min_str[0]=0;

  size_t min_length, max_length;
  field_length-= maybe_null;
  /* If the item is a LIKE, use its escape, otherwise use backslash */
  int escape= type == Item_func::LIKE_FUNC ?
    ((Item_func_like *) item)->escape : '\\';
  if (field->charset()->like_range(res->ptr(), res->length(),
                                   escape, wild_one, wild_many,
                                   field_length,
                                   (char*) min_str + offset,
                                   (char*) max_str + offset,
                                   &min_length, &max_length))
    DBUG_RETURN(0);              // Can't optimize with LIKE

  if (offset != maybe_null)			// BLOB or VARCHAR
  {
    int2store(min_str + maybe_null, min_length);
    int2store(max_str + maybe_null, max_length);
  }
  SEL_ARG *tree= new (param->mem_root) SEL_ARG(field, min_str, max_str);
  DBUG_RETURN(tree);
}


SEL_TREE *
Item_bool_func::get_mm_parts(RANGE_OPT_PARAM *param, Field *field,
	                     Item_func::Functype type, Item *value)
{
  DBUG_ENTER("get_mm_parts");
  if (field->table != param->table)
    DBUG_RETURN(0);

  KEY_PART *key_part = param->key_parts;
  KEY_PART *end = param->key_parts_end;
  SEL_TREE *tree=0;
  table_map value_used_tables= 0;
  bool know_sargable_substr= false;
  bool sargable_substr; // protected by know_sargable_substr

  if (value &&
      (value_used_tables= value->used_tables()) &
      ~(param->prev_tables | param->read_tables))
    DBUG_RETURN(0);
  for (; key_part != end ; key_part++)
  {
    if (field->eq(key_part->field))
    {
      SEL_ARG *sel_arg=0;
      if (!tree && !(tree=new (param->thd->mem_root) SEL_TREE(param->mem_root,
                                                              param->keys)))
	DBUG_RETURN(0);				// OOM
      if (!value || !(value_used_tables & ~param->read_tables))
      {
        /*
          We need to restore the runtime mem_root of the thread in this
          function because it evaluates the value of its argument, while
          the argument can be any, e.g. a subselect. The subselect
          items, in turn, assume that all the memory allocated during
          the evaluation has the same life span as the item itself.
          TODO: opt_range.cc should not reset thd->mem_root at all.
        */
        MEM_ROOT *tmp_root= param->mem_root;
        param->thd->mem_root= param->old_root;
        if (!know_sargable_substr)
        {
          sargable_substr= with_sargable_substr();
          know_sargable_substr= true;
        }
        if (sargable_substr)
        {
          sel_arg= get_mm_leaf_for_LIKE(this, param, key_part->field, key_part,
                                        type, value);
        }
        else
          sel_arg= get_mm_leaf(param, key_part->field, key_part, type, value);
        param->thd->mem_root= tmp_root;

	if (!sel_arg)
	  continue;
	if (sel_arg->type == SEL_ARG::IMPOSSIBLE)
	{
	  tree->type=SEL_TREE::IMPOSSIBLE;
	  DBUG_RETURN(tree);
	}
      }
      else
      {
	// This key may be used later
	if (!(sel_arg= new SEL_ARG(SEL_ARG::MAYBE_KEY)))
	  DBUG_RETURN(0);			// OOM
      }
      sel_arg->part=(uchar) key_part->part;
      sel_arg->max_part_no= sel_arg->part+1;
      tree->keys[key_part->key]=sel_add(tree->keys[key_part->key],sel_arg);
      tree->keys_map.set_bit(key_part->key);
    }
  }

  if (tree && tree->merges.is_empty() && tree->keys_map.is_clear_all())
    tree= NULL;
  DBUG_RETURN(tree);
}


SEL_ARG *
Item_func_null_predicate::get_mm_leaf(RANGE_OPT_PARAM *param,
                                      Field *field, KEY_PART *key_part,
                                      Item_func::Functype type,
                                      Item *value)
{
  MEM_ROOT *alloc= param->mem_root;
  DBUG_ENTER("Item_func_null_predicate::get_mm_leaf");
  DBUG_ASSERT(!value);
  /*
    No check for field->table->maybe_null. It's perfectly fine to use range
    access for cases like

      SELECT * FROM t1 LEFT JOIN t2 ON t2.key IS [NOT] NULL

    ON expression is evaluated before considering NULL-complemented rows, so
    IS [NOT] NULL has regular semantics.
  */
  if (!field->real_maybe_null())
    DBUG_RETURN(type == ISNULL_FUNC ? &null_element : NULL);
  SEL_ARG *tree;
  if (!(tree= new (alloc) SEL_ARG(field, is_null_string, is_null_string)))
    DBUG_RETURN(0);
  if (type == Item_func::ISNOTNULL_FUNC)
  {
    tree->min_flag=NEAR_MIN;		    /* IS NOT NULL ->  X > NULL */
    tree->max_flag=NO_MAX_RANGE;
  }
  DBUG_RETURN(tree);
}


SEL_ARG *
Item_func_truth::get_mm_leaf(RANGE_OPT_PARAM *param,
                             Field *field, KEY_PART *key_part,
                             Item_func::Functype type,
                             Item *value)
{
  MEM_ROOT *alloc= param->mem_root;
  DBUG_ENTER("Item_func_truth::get_mm_leaf");
  if (value) // Affirmative: x IS {FALSE|TRUE}
    DBUG_RETURN(Item_bool_func::get_mm_leaf(param, field, key_part,
                                            type, value));
  DBUG_ASSERT(!affirmative); // x IS NOT {FALSE|TRUE}
  /*
    No check for field->table->maybe_null.
     See comments in Item_func_null_predicate::get_mm_leaf()
  */
  if (!field->real_maybe_null())
    DBUG_RETURN(&null_element);
  DBUG_RETURN(new (alloc) SEL_ARG(field, is_null_string, is_null_string));
}


SEL_ARG *
Item_func_like::get_mm_leaf(RANGE_OPT_PARAM *param,
                            Field *field, KEY_PART *key_part,
                            Item_func::Functype type, Item *value)
{
  DBUG_ENTER("Item_func_like::get_mm_leaf");
  DBUG_RETURN(get_mm_leaf_for_LIKE(this, param, field, key_part, type, value));
}


SEL_ARG *
Item_bool_func::get_mm_leaf(RANGE_OPT_PARAM *param,
                            Field *field, KEY_PART *key_part,
                            Item_func::Functype functype, Item *value)
{
  DBUG_ENTER("Item_bool_func::get_mm_leaf");
  DBUG_ASSERT(value); // IS NULL and IS NOT NULL are handled separately
  if (key_part->image_type != Field::itRAW)
    DBUG_RETURN(0);   // e.g. SPATIAL index
  DBUG_RETURN(field->get_mm_leaf(param, key_part, this,
                                 functype_to_scalar_comparison_op(functype),
                                 value));
}


Data_type_compatibility
Field::can_optimize_scalar_range(const RANGE_OPT_PARAM *param,
                                 const KEY_PART *key_part,
                                 const Item_bool_func *cond,
                                 scalar_comparison_op op,
                                 Item *value) const
{
  bool is_eq_func= op == SCALAR_CMP_EQ || op == SCALAR_CMP_EQUAL;
  uint keynr= param->real_keynr[key_part->key];
  if (param->using_real_indexes &&
      !optimize_range(keynr, key_part->part) && !is_eq_func)
    return Data_type_compatibility::INCOMPATIBLE_DATA_TYPE;
  Data_type_compatibility compat= can_optimize_range(cond, value, is_eq_func);
  if (compat == Data_type_compatibility::OK)
    return compat;
  /*
    Raise a note that the index part could not be used.

    TODO: Perhaps we also need to raise a similar note when
    a partition could not be used (when using_real_indexes==false).
  */
  if (param->using_real_indexes && param->note_unusable_keys &&
      (param->note_unusable_keys & cond->bitmap_bit()))
  {
    DBUG_ASSERT(keynr < table->s->keys);
    /*
      Here "cond" can be any sargable predicate, e.g.:
      1. field=value (and other scalar comparison predicates: <, <=, <=>, =>, >)
      2. field [NOT] BETWEEN value1 AND value2
      3. field [NOT] IN (value1, value2...)
      Don't print the entire "cond" as in case of BETWEEN and IN
      it would list all values.
      Let's only print the current field/value pair.
    */
    raise_note_cannot_use_key_part(param->thd, keynr, key_part->part,
                                   scalar_comparison_op_to_lex_cstring(op),
                                   cond->compare_collation(),
                                   value, compat);
  }
  return compat;
}


uchar *Field::make_key_image(MEM_ROOT *mem_root, const KEY_PART *key_part)
{
  DBUG_ENTER("Field::make_key_image");
  uint maybe_null= (uint) real_maybe_null();
  uchar *str;
  if (!(str= (uchar*) alloc_root(mem_root, key_part->store_length + 1)))
    DBUG_RETURN(0);
  if (maybe_null)
    *str= (uchar) is_real_null();        // Set to 1 if null
  get_key_image(str + maybe_null, key_part->length, key_part->image_type);
  DBUG_RETURN(str);
}


SEL_ARG *Field::stored_field_make_mm_leaf_truncated(RANGE_OPT_PARAM *param,
                                                    scalar_comparison_op op,
                                                    Item *value)
{
  DBUG_ENTER("Field::stored_field_make_mm_leaf_truncated");
  if ((op == SCALAR_CMP_EQ || op == SCALAR_CMP_EQUAL) &&
      value->result_type() == item_cmp_type(result_type(),
                                            value->result_type()))
    DBUG_RETURN(new (param->mem_root) SEL_ARG_IMPOSSIBLE(this));
  /*
    TODO: We should return trees of the type SEL_ARG::IMPOSSIBLE
    for the cases like int_field > 999999999999999999999999 as well.
  */
  DBUG_RETURN(0);
}


SEL_ARG *Field_num::get_mm_leaf(RANGE_OPT_PARAM *prm, KEY_PART *key_part,
                                const Item_bool_func *cond,
                                scalar_comparison_op op, Item *value)
{
  DBUG_ENTER("Field_num::get_mm_leaf");
  if (can_optimize_scalar_range(prm, key_part, cond, op, value) !=
      Data_type_compatibility::OK)
    DBUG_RETURN(0);
  int err= value->save_in_field_no_warnings(this, 1);
  if ((op != SCALAR_CMP_EQUAL && is_real_null()) || err < 0)
    DBUG_RETURN(&null_element);
  if (err > 0 && cmp_type() != value->result_type())
    DBUG_RETURN(stored_field_make_mm_leaf_truncated(prm, op, value));
  DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
}


SEL_ARG *Field_temporal::get_mm_leaf(RANGE_OPT_PARAM *prm, KEY_PART *key_part,
                                     const Item_bool_func *cond,
                                     scalar_comparison_op op, Item *value)
{
  DBUG_ENTER("Field_temporal::get_mm_leaf");
  if (can_optimize_scalar_range(prm, key_part, cond, op, value) !=
      Data_type_compatibility::OK)
    DBUG_RETURN(0);
  int err= value->save_in_field_no_warnings(this, 1);
  if ((op != SCALAR_CMP_EQUAL && is_real_null()) || err < 0)
    DBUG_RETURN(&null_element);
  if (err > 0)
    DBUG_RETURN(stored_field_make_mm_leaf_truncated(prm, op, value));
  DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
}


SEL_ARG *Field_date_common::get_mm_leaf(RANGE_OPT_PARAM *prm,
                                        KEY_PART *key_part,
                                        const Item_bool_func *cond,
                                        scalar_comparison_op op,
                                        Item *value)
{
  DBUG_ENTER("Field_date_common::get_mm_leaf");
  if (can_optimize_scalar_range(prm, key_part, cond, op, value) !=
      Data_type_compatibility::OK)
    DBUG_RETURN(0);
  int err= value->save_in_field_no_warnings(this, 1);
  if ((op != SCALAR_CMP_EQUAL && is_real_null()) || err < 0)
    DBUG_RETURN(&null_element);
  if (err > 0)
  {
    if (err == 3)
    {
      /*
        We were saving DATETIME into a DATE column, the conversion went ok
        but a non-zero time part was cut off.

        In MySQL's SQL dialect, DATE and DATETIME are compared as datetime
        values. Index over a DATE column uses DATE comparison. Changing
        from one comparison to the other is possible:

        datetime(date_col)< '2007-12-10 12:34:55' -> date_col<='2007-12-10'
        datetime(date_col)<='2007-12-10 12:34:55' -> date_col<='2007-12-10'

        datetime(date_col)> '2007-12-10 12:34:55' -> date_col>='2007-12-10'
        datetime(date_col)>='2007-12-10 12:34:55' -> date_col>='2007-12-10'

        but we'll need to convert '>' to '>=' and '<' to '<='. This will
        be done together with other types at the end of this function
        (grep for stored_field_cmp_to_item)
      */
      if (op == SCALAR_CMP_EQ || op == SCALAR_CMP_EQUAL)
        DBUG_RETURN(new (prm->mem_root) SEL_ARG_IMPOSSIBLE(this));
      DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
    }
    DBUG_RETURN(stored_field_make_mm_leaf_truncated(prm, op, value));
  }
  DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
}


SEL_ARG *Field_str::get_mm_leaf(RANGE_OPT_PARAM *prm, KEY_PART *key_part,
                                const Item_bool_func *cond,
                                scalar_comparison_op op, Item *value)
{
  int err;
  DBUG_ENTER("Field_str::get_mm_leaf");
  if (can_optimize_scalar_range(prm, key_part, cond, op, value) !=
      Data_type_compatibility::OK)
    DBUG_RETURN(0);

  {
    /*
      Do CharsetNarrowing if necessary
      This means that we are temporary changing the character set of the
      current key field to make key lookups possible.
      This is needed when comparing an utf8mb3 key field with an utf8mb4 value.
      See cset_narrowing.h for more details.
    */
    bool do_narrowing=
      Utf8_narrow::should_do_narrowing(this, value->collation.collation);
    Utf8_narrow narrow(this, do_narrowing);

    err= value->save_in_field_no_warnings(this, 1);
    narrow.stop();
  }

  if ((op != SCALAR_CMP_EQUAL && is_real_null()) || err < 0)
    DBUG_RETURN(&null_element);
  if (err > 0)
  {
    if (op == SCALAR_CMP_EQ || op == SCALAR_CMP_EQUAL)
      DBUG_RETURN(new (prm->mem_root) SEL_ARG_IMPOSSIBLE(this));
    DBUG_RETURN(NULL); /*  Cannot infer anything */
  }
  DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
}


SEL_ARG *Field::get_mm_leaf_int(RANGE_OPT_PARAM *prm, KEY_PART *key_part,
                                const Item_bool_func *cond,
                                scalar_comparison_op op, Item *value,
                                bool unsigned_field)
{
  DBUG_ENTER("Field::get_mm_leaf_int");
  if (can_optimize_scalar_range(prm, key_part, cond, op, value) !=
      Data_type_compatibility::OK)
    DBUG_RETURN(0);
  int err= value->save_in_field_no_warnings(this, 1);
  if ((op != SCALAR_CMP_EQUAL && is_real_null()) || err < 0)
    DBUG_RETURN(&null_element);
  if (err > 0)
  {
    if (value->result_type() != INT_RESULT)
      DBUG_RETURN(stored_field_make_mm_leaf_truncated(prm, op, value));
    else
      DBUG_RETURN(stored_field_make_mm_leaf_bounded_int(prm, key_part,
                                                        op, value,
                                                        unsigned_field));
  }
  if (value->result_type() != INT_RESULT)
    DBUG_RETURN(stored_field_make_mm_leaf(prm, key_part, op, value));
  DBUG_RETURN(stored_field_make_mm_leaf_exact(prm, key_part, op, value));
}


/*
  This method is called when:
  - value->save_in_field_no_warnings() returned err > 0
  - and both field and "value" are of integer data types
  If an integer got bounded (e.g. to within 0..255 / -128..127)
  for < or >, set flags as for <= or >= (no NEAR_MAX / NEAR_MIN)
*/

SEL_ARG *Field::stored_field_make_mm_leaf_bounded_int(RANGE_OPT_PARAM *param,
                                                      KEY_PART *key_part,
                                                      scalar_comparison_op op,
                                                      Item *value,
                                                      bool unsigned_field)
{
  DBUG_ENTER("Field::stored_field_make_mm_leaf_bounded_int");
  if (op == SCALAR_CMP_EQ || op == SCALAR_CMP_EQUAL) // e.g. tinyint = 200
    DBUG_RETURN(new (param->mem_root) SEL_ARG_IMPOSSIBLE(this));
  longlong item_val= value->val_int();

  if (op == SCALAR_CMP_LT && ((item_val > 0)
                   || (value->unsigned_flag && (ulonglong)item_val > 0 )))
    op= SCALAR_CMP_LE; // e.g. rewrite (tinyint < 200) to (tinyint <= 127)
  else if (op == SCALAR_CMP_GT && !unsigned_field &&
           !value->unsigned_flag && item_val < 0)
    op= SCALAR_CMP_GE; // e.g. rewrite (tinyint > -200) to (tinyint >= -128)

  /*
    Check if we are comparing an UNSIGNED integer with a negative constant.
    In this case we know that:
    (a) (unsigned_int [< | <=] negative_constant) == FALSE
    (b) (unsigned_int [> | >=] negative_constant) == TRUE
    In case (a) the condition is false for all values, and in case (b) it
    is true for all values, so we can avoid unnecessary retrieval and condition
    testing, and we also get correct comparison of unsinged integers with
    negative integers (which otherwise fails because at query execution time
    negative integers are cast to unsigned if compared with unsigned).
   */
  if (unsigned_field && !value->unsigned_flag && item_val < 0)
  {
    if (op == SCALAR_CMP_LT || op == SCALAR_CMP_LE) // e.g. uint < -1
      DBUG_RETURN(new (param->mem_root) SEL_ARG_IMPOSSIBLE(this));
    if (op == SCALAR_CMP_GT || op == SCALAR_CMP_GE) // e.g. uint > -1
      DBUG_RETURN(0);
  }
  DBUG_RETURN(stored_field_make_mm_leaf_exact(param, key_part, op, value));
}


SEL_ARG *Field::stored_field_make_mm_leaf(RANGE_OPT_PARAM *param,
                                          KEY_PART *key_part,
                                          scalar_comparison_op op,
                                          Item *value)
{
  DBUG_ENTER("Field::stored_field_make_mm_leaf");
  THD *thd= param->thd;
  MEM_ROOT *mem_root= param->mem_root;
  uchar *str;
  if (!(str= make_key_image(param->mem_root, key_part)))
    DBUG_RETURN(0);

  switch (op) {
  case SCALAR_CMP_LE:
    DBUG_RETURN(new (mem_root) SEL_ARG_LE(str, this));
  case SCALAR_CMP_LT:
    DBUG_RETURN(new (mem_root) SEL_ARG_LT(thd, str, key_part, this, value));
  case SCALAR_CMP_GT:
    DBUG_RETURN(new (mem_root) SEL_ARG_GT(thd, str, key_part, this, value));
  case SCALAR_CMP_GE:
    DBUG_RETURN(new (mem_root) SEL_ARG_GE(thd, str, key_part, this, value));
  case SCALAR_CMP_EQ:
  case SCALAR_CMP_EQUAL:
    DBUG_RETURN(new (mem_root) SEL_ARG(this, str, str));
    break;
  }
  DBUG_ASSERT(0);
  DBUG_RETURN(NULL);
}


SEL_ARG *Field::stored_field_make_mm_leaf_exact(RANGE_OPT_PARAM *param,
                                                KEY_PART *key_part,
                                                scalar_comparison_op op,
                                                Item *value)
{
  DBUG_ENTER("Field::stored_field_make_mm_leaf_exact");
  uchar *str;
  if (!(str= make_key_image(param->mem_root, key_part)))
    DBUG_RETURN(0);

  switch (op) {
  case SCALAR_CMP_LE:
    DBUG_RETURN(new (param->mem_root) SEL_ARG_LE(str, this));
  case SCALAR_CMP_LT:
    DBUG_RETURN(new (param->mem_root) SEL_ARG_LT(str, key_part, this));
  case SCALAR_CMP_GT:
    DBUG_RETURN(new (param->mem_root) SEL_ARG_GT(str, key_part, this));
  case SCALAR_CMP_GE:
    DBUG_RETURN(new (param->mem_root) SEL_ARG_GE(str, this));
  case SCALAR_CMP_EQ:
  case SCALAR_CMP_EQUAL:
    DBUG_RETURN(new (param->mem_root) SEL_ARG(this, str, str));
    break;
  }
  DBUG_ASSERT(0);
  DBUG_RETURN(NULL);
}


/******************************************************************************
** Tree manipulation functions
** If tree is 0 it means that the condition can't be tested. It refers
** to a non existent table or to a field in current table with isn't a key.
** The different tree flags:
** IMPOSSIBLE:	 Condition is never TRUE
** ALWAYS:	 Condition is always TRUE
** MAYBE:	 Condition may exists when tables are read
** MAYBE_KEY:	 Condition refers to a key that may be used in join loop
** KEY_RANGE:	 Condition uses a key
******************************************************************************/

/*
  Update weights for SEL_ARG graph that is connected only via next_key_part
  (and not left/right) links
*/
static uint update_weight_for_single_arg(SEL_ARG *arg)
{
  if (arg->next_key_part)
    return (arg->weight= 1 + update_weight_for_single_arg(arg->next_key_part));
  else
    return (arg->weight= 1);
}


/*
  Add a new key test to a key when scanning through all keys
  This will never be called for same key parts.
*/

static SEL_ARG *
sel_add(SEL_ARG *key1,SEL_ARG *key2)
{
  SEL_ARG *root,**key_link;

  if (!key1)
    return key2;
  if (!key2)
    return key1;

  key_link= &root;
  while (key1 && key2)
  {
    if (key1->part < key2->part)
    {
      *key_link= key1;
      key_link= &key1->next_key_part;
      key1=key1->next_key_part;
    }
    else
    {
      *key_link= key2;
      key_link= &key2->next_key_part;
      key2=key2->next_key_part;
    }
  }
  *key_link=key1 ? key1 : key2;

  update_weight_for_single_arg(root);
  return root;
}


/* 
  Build a range tree for the conjunction of the range parts of two trees

  SYNOPSIS
    and_range_trees()
      param           Context info for the operation
      tree1           SEL_TREE for the first conjunct          
      tree2           SEL_TREE for the second conjunct
      result          SEL_TREE for the result

  DESCRIPTION
    This function takes range parts of two trees tree1 and tree2 and builds
    a range tree for the conjunction of the formulas that these two range parts
    represent.
    More exactly: 
    if the range part of tree1 represents the normalized formula 
      R1_1 AND ... AND R1_k,
    and the range part of tree2 represents the normalized formula
      R2_1 AND ... AND R2_k,
    then the range part of the result represents the formula:
     RT = R_1 AND ... AND R_k, where R_i=(R1_i AND R2_i) for each i from [1..k]

    The function assumes that tree1 is never equal to tree2. At the same
    time the tree result can be the same as tree1 (but never as tree2).
    If result==tree1 then rt replaces the range part of tree1 leaving
    imerges as they are.
    if result!=tree1 than it is assumed that the SEL_ARG trees in tree1 and
    tree2 should be preserved. Otherwise they can be destroyed.

  RETURN 
    1    if the type the result tree is  SEL_TREE::IMPOSSIBLE
    0    otherwise    
*/

static
int and_range_trees(RANGE_OPT_PARAM *param, SEL_TREE *tree1, SEL_TREE *tree2,
                    SEL_TREE *result)
{
  DBUG_ENTER("and_ranges");
  key_map  result_keys;
  result_keys.clear_all();
  key_map anded_keys= tree1->keys_map;
  anded_keys.merge(tree2->keys_map);
  int key_no;
  key_map::Iterator it(anded_keys);
  while ((key_no= it++) != key_map::Iterator::BITMAP_END)
  {
    uint flag=0;
    SEL_ARG *key1= tree1->keys[key_no];
    SEL_ARG *key2= tree2->keys[key_no];
    if (key1 && !key1->simple_key())
      flag|= CLONE_KEY1_MAYBE;
    if (key2 && !key2->simple_key())
      flag|=CLONE_KEY2_MAYBE;
    if (result != tree1)
    { 
      if (key1)
        key1->incr_refs();
      if (key2)
        key2->incr_refs();
    }
    SEL_ARG *key;
    if ((result->keys[key_no]= key= key_and_with_limit(param, key_no,
                                                       key1, key2, flag)))
    {
      if (key && key->type == SEL_ARG::IMPOSSIBLE)
      {
	result->type= SEL_TREE::IMPOSSIBLE;
        if (param->using_real_indexes)
        {
          param->table->with_impossible_ranges.set_bit(param->
                                                       real_keynr[key_no]);
        }
        DBUG_RETURN(1);
      }
      result_keys.set_bit(key_no);
#ifdef EXTRA_DEBUG
      if (param->alloced_sel_args <
          param->thd->variables.optimizer_max_sel_args)
        key->test_use_count(key);
#endif
    }
  }
  result->keys_map= result_keys;
  DBUG_RETURN(0);
}
  

/*
  Build a SEL_TREE for a conjunction out of such trees for the conjuncts

  SYNOPSIS
    tree_and()
      param           Context info for the operation
      tree1           SEL_TREE for the first conjunct          
      tree2           SEL_TREE for the second conjunct

  DESCRIPTION
    This function builds a tree for the formula (A AND B) out of the trees
    tree1 and tree2 that has been built for the formulas A and B respectively.

    In a general case
      tree1 represents the formula RT1 AND MT1,
        where RT1 = R1_1 AND ... AND R1_k1, MT1=M1_1 AND ... AND M1_l1;
      tree2 represents the formula RT2 AND MT2 
        where RT2 = R2_1 AND ... AND R2_k2, MT2=M2_1 AND ... AND M2_l2.

    The result tree will represent the formula of the following structure:
      RT AND RT1MT2 AND RT2MT1, such that
        rt is a tree obtained by range intersection of trees tree1 and tree2,
        RT1MT2 = RT1M2_1 AND ... AND RT1M2_l2,
        RT2MT1 = RT2M1_1 AND ... AND RT2M1_l1,
        where rt1m2_i (i=1,...,l2) is the result of the pushdown operation
        of range tree rt1 into imerge m2_i, while rt2m1_j (j=1,...,l1) is the
        result of the pushdown operation of range tree rt2 into imerge m1_j.

    RT1MT2/RT2MT is empty if MT2/MT1 is empty.
 
    The range intersection of two range trees is produced by the function
    and_range_trees. The pushdown of a range tree to a imerge is performed
    by the function imerge_list_and_tree. This function may produce imerges
    containing only one range tree. Such trees are intersected with rt and 
    the result of intersection is returned as the range part of the result
    tree, while the corresponding imerges are removed altogether from its
    imerge part. 
    
  NOTE
    The pushdown operation of range trees into imerges is needed to be able
    to construct valid imerges for the condition like this:
      key1_p1=c1 AND (key1_p2 BETWEEN c21 AND c22 OR key2 < c2)

  NOTE
    Currently we do not support intersection between indexes and index merges.
    When this will be supported the list of imerges for the result tree
    should include also imerges from M1 and M2. That's why an extra parameter
    is added to the function imerge_list_and_tree. If we call the function
    with the last parameter equal to FALSE then MT1 and MT2 will be preserved
    in the imerge list of the result tree. This can lead to the exponential
    growth of the imerge list though. 
    Currently the last parameter of imerge_list_and_tree calls is always
    TRUE.

  RETURN
    The result tree, if a success
    0 - otherwise.        
*/

static 
SEL_TREE *tree_and(RANGE_OPT_PARAM *param, SEL_TREE *tree1, SEL_TREE *tree2)
{
  DBUG_ENTER("tree_and");
  if (!tree1)
    DBUG_RETURN(tree2);
  if (!tree2)
    DBUG_RETURN(tree1);
  if (tree1->type == SEL_TREE::IMPOSSIBLE || tree2->type == SEL_TREE::ALWAYS)
    DBUG_RETURN(tree1);
  if (tree2->type == SEL_TREE::IMPOSSIBLE || tree1->type == SEL_TREE::ALWAYS)
    DBUG_RETURN(tree2);
  if (tree1->type == SEL_TREE::MAYBE)
  {
    if (tree2->type == SEL_TREE::KEY)
      tree2->type=SEL_TREE::KEY_SMALLER;
    DBUG_RETURN(tree2);
  }
  if (tree2->type == SEL_TREE::MAYBE)
  {
    tree1->type=SEL_TREE::KEY_SMALLER;
    DBUG_RETURN(tree1);
  }

  if (!tree1->merges.is_empty())
    imerge_list_and_tree(param, &tree1->merges, tree2, TRUE);
  if (!tree2->merges.is_empty())
    imerge_list_and_tree(param, &tree2->merges, tree1, TRUE);
  if (and_range_trees(param, tree1, tree2, tree1))
    DBUG_RETURN(tree1);
  imerge_list_and_list(&tree1->merges, &tree2->merges);
  eliminate_single_tree_imerges(param, tree1);
  DBUG_RETURN(tree1);
}


/*
  Eliminate single tree imerges in a SEL_TREE objects

  SYNOPSIS
    eliminate_single_tree_imerges()
      param      Context info for the function
      tree       SEL_TREE where single tree imerges are to be eliminated 

  DESCRIPTION
    For each imerge in 'tree' that contains only one disjunct tree, i.e.
    for any imerge of the form m=rt, the function performs and operation
    the range part of tree, replaces rt the with the result of anding and
    removes imerge m from the merge part of 'tree'.

  RETURN VALUE
    none          
*/

static
void eliminate_single_tree_imerges(RANGE_OPT_PARAM *param, SEL_TREE *tree)
{
  SEL_IMERGE *imerge;
  List<SEL_IMERGE> merges= tree->merges;
  List_iterator<SEL_IMERGE> it(merges);
  tree->merges.empty();
  while ((imerge= it++))
  {
    if (imerge->trees+1 == imerge->trees_next)
    {
      tree= tree_and(param, tree, *imerge->trees);
      it.remove();
    }
  }
  tree->merges= merges;
} 


/*
  For two trees check that there are indexes with ranges in both of them  
 
  SYNOPSIS
    sel_trees_have_common_keys()
      tree1           SEL_TREE for the first tree
      tree2           SEL_TREE for the second tree
      common_keys OUT bitmap of all indexes with ranges in both trees

  DESCRIPTION
    For two trees tree1 and tree1 the function checks if there are indexes
    in their range parts such that SEL_ARG trees are defined for them in the
    range parts of both trees. The function returns the bitmap of such 
    indexes in the parameter common_keys.

  RETURN 
    TRUE    if there are such indexes (common_keys is nor empty)
    FALSE   otherwise
*/

static
bool sel_trees_have_common_keys(SEL_TREE *tree1, SEL_TREE *tree2, 
                                key_map *common_keys)
{
  *common_keys= tree1->keys_map;
  common_keys->intersect(tree2->keys_map);
  return !common_keys->is_clear_all();
}


/*
  Check whether range parts of two trees can be ored for some indexes

  SYNOPSIS
    sel_trees_can_be_ored()
      param              Context info for the function
      tree1              SEL_TREE for the first tree
      tree2              SEL_TREE for the second tree
      common_keys IN/OUT IN: bitmap of all indexes with SEL_ARG in both trees
                        OUT: bitmap of all indexes that can be ored

  DESCRIPTION
    For two trees tree1 and tree2 and the bitmap common_keys containing
    bits for indexes that have SEL_ARG trees in range parts of both trees
    the function checks if there are indexes for which SEL_ARG trees can
    be ored. Two SEL_ARG trees for the same index can be ored if the most
    major components of the index used in these trees coincide. If the 
    SEL_ARG trees for an index cannot be ored the function clears the bit
    for this index in the bitmap common_keys.

    The function does not verify that indexes marked in common_keys really
    have SEL_ARG trees in both tree1 and tree2. It assumes that this is true.

  NOTE
    The function sel_trees_can_be_ored is usually used in pair with the
    function sel_trees_have_common_keys.

  RETURN
    TRUE    if there are indexes for which SEL_ARG trees can be ored 
    FALSE   otherwise
*/

static
bool sel_trees_can_be_ored(RANGE_OPT_PARAM* param,
                           SEL_TREE *tree1, SEL_TREE *tree2, 
                           key_map *common_keys)
{
  DBUG_ENTER("sel_trees_can_be_ored");
  if (!sel_trees_have_common_keys(tree1, tree2, common_keys))
    DBUG_RETURN(FALSE);
  int key_no;
  key_map::Iterator it(*common_keys);
  while ((key_no= it++) != key_map::Iterator::BITMAP_END)
  {
    DBUG_ASSERT(tree1->keys[key_no] && tree2->keys[key_no]);
    /* Trees have a common key, check if they refer to the same key part */
    if (tree1->keys[key_no]->part != tree2->keys[key_no]->part)
      common_keys->clear_bit(key_no);
  }
  DBUG_RETURN(!common_keys->is_clear_all());
}

/*
  Check whether the key parts inf_init..inf_end-1 of one index can compose
  an infix for the key parts key_init..key_end-1 of another index
*/

static
bool is_key_infix(KEY_PART *key_init, KEY_PART *key_end,
                  KEY_PART *inf_init, KEY_PART *inf_end)
{
  KEY_PART *key_part, *inf_part;
  for (key_part= key_init; key_part < key_end; key_part++)
  {
    if (key_part->field->eq(inf_init->field))
      break;
  }
  if (key_part == key_end)
    return false;
  for (key_part++, inf_part= inf_init + 1;
       key_part < key_end && inf_part < inf_end;
       key_part++, inf_part++)
  { 
    if (!key_part->field->eq(inf_part->field))
      return false;
  }
  return inf_part == inf_end;
}


/*
  Check whether range parts of two trees must be ored for some indexes

  SYNOPSIS
    sel_trees_must_be_ored()
      param              Context info for the function
      tree1              SEL_TREE for the first tree
      tree2              SEL_TREE for the second tree
      ordable_keys       bitmap of SEL_ARG trees that can be ored

  DESCRIPTION
    For two trees tree1 and tree2 the function checks whether they must be
    ored. The function assumes that the bitmap ordable_keys contains bits for
    those corresponding pairs of SEL_ARG trees from tree1 and tree2 that can
    be ored.
    We believe that tree1 and tree2 must be ored if any pair of SEL_ARG trees
    r1 and r2, such that r1 is from tree1 and r2 is from tree2 and both
    of them are marked in ordable_keys, can be merged.
    
  NOTE
    The function sel_trees_must_be_ored as a rule is used in pair with the
    function sel_trees_can_be_ored.

  RETURN
    TRUE    if there are indexes for which SEL_ARG trees must be ored 
    FALSE   otherwise
*/

static
bool sel_trees_must_be_ored(RANGE_OPT_PARAM* param,
                            SEL_TREE *tree1, SEL_TREE *tree2,
                            key_map oredable_keys)
{
  key_map tmp;
  DBUG_ENTER("sel_trees_must_be_ored");

  tmp= tree1->keys_map;
  tmp.merge(tree2->keys_map);
  tmp.subtract(oredable_keys);
  if (!tmp.is_clear_all())
    DBUG_RETURN(FALSE);

  int idx1, idx2;
  key_map::Iterator it1(oredable_keys);
  while ((idx1= it1++) != key_map::Iterator::BITMAP_END)
  {
    KEY_PART *key1_init= param->key[idx1]+tree1->keys[idx1]->part;
    KEY_PART *key1_end= param->key[idx1]+tree1->keys[idx1]->max_part_no;
    key_map::Iterator it2(oredable_keys);
    while ((idx2= it2++) != key_map::Iterator::BITMAP_END)
    {
      if (idx2 <= idx1)
        continue;
      
      KEY_PART *key2_init= param->key[idx2]+tree2->keys[idx2]->part;
      KEY_PART *key2_end= param->key[idx2]+tree2->keys[idx2]->max_part_no;
      if (!is_key_infix(key1_init, key1_end, key2_init, key2_end) &&
          !is_key_infix(key2_init, key2_end, key1_init, key1_end))
        DBUG_RETURN(FALSE);
    }
  }
      
  DBUG_RETURN(TRUE);
}  


/*
  Remove the trees that are not suitable for record retrieval

  SYNOPSIS
    remove_nonrange_trees()
      param  Context info for the function
      tree   Tree to be processed, tree->type is KEY or KEY_SMALLER

  DESCRIPTION
    This function walks through tree->keys[] and removes the SEL_ARG* trees
    that are not "maybe" trees (*) and cannot be used to construct quick range
    selects.
    (*) - have type MAYBE or MAYBE_KEY. Perhaps we should remove trees of
          these types here as well.

    A SEL_ARG* tree cannot be used to construct quick select if it has
    tree->part != 0. (e.g. it could represent "keypart2 < const").

    Normally we allow construction of SEL_TREE objects that have SEL_ARG
    trees that do not allow quick range select construction.
    For example:
    for " keypart1=1 AND keypart2=2 " the execution will proceed as follows:
    tree1= SEL_TREE { SEL_ARG{keypart1=1} }
    tree2= SEL_TREE { SEL_ARG{keypart2=2} } -- can't make quick range select
                                               from this
    call tree_and(tree1, tree2) -- this joins SEL_ARGs into a usable SEL_ARG
                                   tree.

    Another example:
    tree3= SEL_TREE { SEL_ARG{key1part1 = 1} }
    tree4= SEL_TREE { SEL_ARG{key2part2 = 2} }  -- can't make quick range select
                                               from this
    call tree_or(tree3, tree4) -- creates a SEL_MERGE ot of which no index
    merge can be constructed, but it is potentially useful, as anding it with
    tree5= SEL_TREE { SEL_ARG{key2part1 = 3} } creates an index merge that
    represents the formula
      key1part1=1 AND key2part1=3 OR key2part1=3 AND key2part2=2
    for which an index merge can be built.

    Any final SEL_TREE may contain SEL_ARG trees for which no quick select
    can be built. Such SEL_ARG trees should be removed from the range part
    before different range scans are evaluated. Such SEL_ARG trees also should
    be removed from all range trees of each index merge before different
    possible index merge plans are evaluated. If after this removal one
    of the range trees in the index merge becomes empty the whole index merge
    must be discarded.

  RETURN
    0  Ok, some suitable trees left
    1  No tree->keys[] left.
*/

static bool remove_nonrange_trees(PARAM *param, SEL_TREE *tree)
{
  bool res= FALSE;

  for (uint i=0; i < param->keys; i++)
  {
    if (!tree->keys[i])
      continue;

    if (tree->keys[i]->part == 0)
    {
      res= TRUE;
      continue;
    }

    /* Mark that records_in_range has not been called */
    param->quick_rows[param->real_keynr[i]]= HA_POS_ERROR;
    tree->keys[i]= nullptr;
    tree->keys_map.clear_bit(i);
  }

  return !res;
}


/*
  Restore nonrange trees to their previous state
*/

static void restore_nonrange_trees(RANGE_OPT_PARAM *param, SEL_TREE *tree,
                                   SEL_ARG **backup_keys)
{
  for (uint i= 0; i < param->keys; i++)
  {
    if (!backup_keys[i])
      continue;

    tree->keys[i]= backup_keys[i];
    tree->keys_map.set_bit(i);
  }
}

/*
  Build a SEL_TREE for a disjunction out of such trees for the disjuncts

  SYNOPSIS
    tree_or()
      param           Context info for the operation
      tree1           SEL_TREE for the first disjunct          
      tree2           SEL_TREE for the second disjunct

  DESCRIPTION
    This function builds a tree for the formula (A OR B) out of the trees
    tree1 and tree2 that has been built for the formulas A and B respectively.

    In a general case
      tree1 represents the formula RT1 AND MT1,
        where RT1=R1_1 AND ... AND R1_k1, MT1=M1_1 AND ... AND M1_l1;
      tree2 represents the formula RT2 AND MT2 
        where RT2=R2_1 AND ... AND R2_k2, MT2=M2_1 and ... and M2_l2.

    The function constructs the result tree according the formula
      (RT1 OR RT2) AND (MT1 OR RT1) AND (MT2 OR RT2) AND (MT1 OR MT2)
    that is equivalent to the formula (RT1 AND MT1) OR (RT2 AND MT2).

    To limit the number of produced imerges the function considers
    a weaker formula than the original one:
      (RT1 AND M1_1) OR (RT2 AND M2_1) 
    that is equivalent to:
      (RT1 OR RT2)                  (1)
        AND 
      (M1_1 OR M2_1)                (2)
        AND
      (M1_1 OR RT2)                 (3)
        AND
      (M2_1 OR RT1)                 (4)

    For the first conjunct (1) the function builds a tree with a range part
    and, possibly, one imerge. For the other conjuncts (2-4)the function
    produces sets of imerges. All constructed imerges are included into the
    result tree.
    
    For the formula (1) the function produces the tree representing a formula  
    of the structure RT [AND M], such that:
     - the range tree rt contains the result of oring SEL_ARG trees from rt1
       and rt2
     - the imerge m consists of two range trees rt1 and rt2.
    The imerge m is added if it's not true that rt1 and rt2 must be ored
    If rt1 and rt2 can't be ored rt is empty and only m is produced for (1).

    To produce imerges for the formula (2) the function calls the function
    imerge_list_or_list passing it the merge parts of tree1 and tree2 as
    parameters.

    To produce imerges for the formula (3) the function calls the function
    imerge_list_or_tree passing it the imerge m1_1 and the range tree rt2 as
    parameters. Similarly, to produce imerges for the formula (4) the function
    calls the function imerge_list_or_tree passing it the imerge m2_1 and the
    range tree rt1.

    If rt1 is empty then the trees for (1) and (4) are empty.
    If rt2 is empty then the trees for (1) and (3) are empty.
    If mt1 is empty then the trees for (2) and (3) are empty.
    If mt2 is empty then the trees for (2) and (4) are empty.

  RETURN
    The result tree for the operation if a success
    0 - otherwise
*/

static SEL_TREE *
tree_or(RANGE_OPT_PARAM *param,SEL_TREE *tree1,SEL_TREE *tree2)
{
  DBUG_ENTER("tree_or");
  if (!tree1 || !tree2)
    DBUG_RETURN(0);
  if (tree1->type == SEL_TREE::IMPOSSIBLE || tree2->type == SEL_TREE::ALWAYS)
    DBUG_RETURN(tree2);
  if (tree2->type == SEL_TREE::IMPOSSIBLE || tree1->type == SEL_TREE::ALWAYS)
    DBUG_RETURN(tree1);
  if (tree1->type == SEL_TREE::MAYBE)
    DBUG_RETURN(tree1);				// Can't use this
  if (tree2->type == SEL_TREE::MAYBE)
    DBUG_RETURN(tree2);

  SEL_TREE *result= NULL;
  key_map ored_keys;
  SEL_TREE *rtree[2]= {NULL,NULL};
  SEL_IMERGE *imerge[2]= {NULL, NULL};
  bool no_ranges1= tree1->without_ranges();
  bool no_ranges2= tree2->without_ranges();
  bool no_merges1= tree1->without_imerges();
  bool no_merges2= tree2->without_imerges();
  if (!no_ranges1 && !no_merges2)
  {
    rtree[0]= new SEL_TREE(tree1, TRUE, param);
    imerge[1]= new SEL_IMERGE(tree2->merges.head(), 0, param);
  }
  if (!no_ranges2 && !no_merges1)
  {
    rtree[1]= new SEL_TREE(tree2, TRUE, param);
    imerge[0]= new SEL_IMERGE(tree1->merges.head(), 0, param);
  }
  bool no_imerge_from_ranges= FALSE;

  /* Build the range part of the tree for the formula (1) */ 
  if (sel_trees_can_be_ored(param, tree1, tree2, &ored_keys))
  {
    bool must_be_ored= sel_trees_must_be_ored(param, tree1, tree2, ored_keys);
    no_imerge_from_ranges= must_be_ored;

    if (no_imerge_from_ranges && no_merges1 && no_merges2)
    {
      /*
        Reuse tree1 as the result in simple cases. This reduces memory usage
        for e.g. "key IN (c1, ..., cN)" which produces a lot of ranges.
      */
      result= tree1;
      result->keys_map.clear_all();
    }
    else
    {
      if (!(result= new (param->mem_root) SEL_TREE(param->mem_root,
                                                   param->keys)))
      {
        DBUG_RETURN(result);
      }
    }

    key_map::Iterator it(ored_keys);
    int key_no;
    while ((key_no= it++) != key_map::Iterator::BITMAP_END)
    {
      SEL_ARG *key1= tree1->keys[key_no];
      SEL_ARG *key2= tree2->keys[key_no];
      if (!must_be_ored)
      {
        key1->incr_refs();
        key2->incr_refs();
      }
      if ((result->keys[key_no]= key_or_with_limit(param, key_no, key1, key2)))
        result->keys_map.set_bit(key_no);
    }
    result->type= tree1->type;
  }
  else
  {
    if (!result && !(result= new (param->mem_root) SEL_TREE(param->mem_root,
                                                            param->keys)))
      DBUG_RETURN(result);
  }

  if (no_imerge_from_ranges && no_merges1 && no_merges2)
  {
    if (result->keys_map.is_clear_all())
      result->type= SEL_TREE::ALWAYS;
    DBUG_RETURN(result);
  }

  /*
    Ok, the result now has the ranges that one gets for (RT1 OR RT2).
    If construction of SEL_IMERGE is disabled, stop right here.
  */
  if (param->disable_index_merge_plans)
    DBUG_RETURN(result);

  SEL_IMERGE *imerge_from_ranges;
  if (!(imerge_from_ranges= new SEL_IMERGE()))
    result= NULL;
  else if (!no_ranges1 && !no_ranges2 && !no_imerge_from_ranges)
  {
    /* Build the imerge part of the tree for the formula (1) */
    SEL_TREE *rt1= tree1;
    SEL_TREE *rt2= tree2;
    if (no_merges1)
      rt1= new SEL_TREE(tree1, TRUE, param);
    if (no_merges2)
      rt2= new SEL_TREE(tree2, TRUE, param);
    if (!rt1 || !rt2 ||
        result->merges.push_back(imerge_from_ranges) ||
        imerge_from_ranges->or_sel_tree(param, rt1) ||
        imerge_from_ranges->or_sel_tree(param, rt2))
      result= NULL;
  }
  if (!result)
    DBUG_RETURN(result);

  result->type= tree1->type;

  if (!no_merges1 && !no_merges2 && 
      !imerge_list_or_list(param, &tree1->merges, &tree2->merges))
  {
    /* Build the imerges for the formula (2) */
    imerge_list_and_list(&result->merges, &tree1->merges);
  }

  /* Build the imerges for the formulas (3) and (4) */
  for (uint i=0; i < 2; i++)
  {
    List<SEL_IMERGE> merges;
    SEL_TREE *rt= rtree[i];
    SEL_IMERGE *im= imerge[1-i];
    
    if (rt && im && !merges.push_back(im) && 
        !imerge_list_or_tree(param, &merges, rt))
      imerge_list_and_list(&result->merges, &merges);
  }
 
  DBUG_RETURN(result);
}


/* And key trees where key1->part < key2 -> part */

static SEL_ARG *
and_all_keys(RANGE_OPT_PARAM *param, SEL_ARG *key1, SEL_ARG *key2, 
             uint clone_flag)
{
  SEL_ARG *next;
  ulong use_count=key1->use_count;

  if (sel_arg_and_weight_heuristic(param, key1, key2))
    return key1;

  if (key1->elements != 1)
  {
    key2->use_count+=key1->elements-1; //psergey: why we don't count that key1 has n-k-p?
    key2->increment_use_count((int) key1->elements-1);
  }
  if (key1->type == SEL_ARG::MAYBE_KEY)
  {
    if (key2->type == SEL_ARG::KEY_RANGE)
      return key2;
    key1->right= key1->left= &null_element;
    key1->next= key1->prev= 0;
    key1->weight= 1 + (key1->next_key_part? key1->next_key_part->weight: 0);
  }

  for (next=key1->first(); next ; next=next->next)
  {
    if (next->next_key_part)
    {
      uint old_weight= next->next_key_part->weight;
      SEL_ARG *tmp= key_and(param, next->next_key_part, key2, clone_flag);
      if (tmp && tmp->type == SEL_ARG::IMPOSSIBLE)
      {
	key1=key1->tree_delete(next);
	continue;
      }
      next->next_key_part=tmp;
      key1->weight+= (tmp? tmp->weight: 0) - old_weight;
      if (use_count)
	next->increment_use_count(use_count);
      if (param->alloced_sel_args >
          param->thd->variables.optimizer_max_sel_args)
        break;
    }
    else
    {
      next->next_key_part=key2;
      key1->weight += key2->weight;
    }
  }
  if (!key1)
    return &null_element;			// Impossible ranges
  key1->use_count++;

  key1->max_part_no= MY_MAX(key2->max_part_no, key2->part+1);
  return key1;
}


/*
  Produce a SEL_ARG graph that represents "key1 AND key2"

  SYNOPSIS
    key_and()
      param   Range analysis context (needed to track if we have allocated
              too many SEL_ARGs)
      key1    First argument, root of its RB-tree
      key2    Second argument, root of its RB-tree

  RETURN
    RB-tree root of the resulting SEL_ARG graph.
    NULL if the result of AND operation is an empty interval {0}.
*/

static SEL_ARG *
key_and(RANGE_OPT_PARAM *param, SEL_ARG *key1, SEL_ARG *key2, uint clone_flag)
{
  if (!key1)
    return key2;
  if (!key2)
    return key1;
  if (key1->part != key2->part)
  {
    if (key1->part > key2->part)
    {
      swap_variables(SEL_ARG *, key1, key2);
      clone_flag=swap_clone_flag(clone_flag);
    }
    // key1->part < key2->part

    if (sel_arg_and_weight_heuristic(param, key1, key2))
      return key1;

    key1->use_count--;
    if (key1->use_count > 0)
      if (!(key1= key1->clone_tree(param)))
	return 0;				// OOM
    return and_all_keys(param, key1, key2, clone_flag);
  }

  if (((clone_flag & CLONE_KEY2_MAYBE) &&
       !(clone_flag & CLONE_KEY1_MAYBE) &&
       key2->type != SEL_ARG::MAYBE_KEY) ||
      key1->type == SEL_ARG::MAYBE_KEY)
  {						// Put simple key in key2
    swap_variables(SEL_ARG *, key1, key2);
    clone_flag=swap_clone_flag(clone_flag);
  }

  /* If one of the key is MAYBE_KEY then the found region may be smaller */
  if (key2->type == SEL_ARG::MAYBE_KEY)
  {
    if (key1->use_count > 1)
    {
      key1->use_count--;
      if (!(key1=key1->clone_tree(param)))
	return 0;				// OOM
      key1->use_count++;
    }
    if (key1->type == SEL_ARG::MAYBE_KEY)
    {						// Both are maybe key
      key1->next_key_part=key_and(param, key1->next_key_part, 
                                  key2->next_key_part, clone_flag);

      key1->weight= 1 + (key1->next_key_part? key1->next_key_part->weight : 0);

      if (key1->next_key_part &&
	  key1->next_key_part->type == SEL_ARG::IMPOSSIBLE)
	return key1;
    }
    else
    {
      key1->maybe_smaller();
      if (key2->next_key_part)
      {
	key1->use_count--;			// Incremented in and_all_keys
        return and_all_keys(param, key1, key2->next_key_part, clone_flag);
      }
      key2->use_count--;			// Key2 doesn't have a tree
    }
    return key1;
  }

  if ((key1->min_flag | key2->min_flag) & GEOM_FLAG)
  {
    /* TODO: why not leave one of the trees? */
    key1->free_tree();
    key2->free_tree();
    return 0;					// Can't optimize this
  }

  key1->use_count--;
  key2->use_count--;
  SEL_ARG *e1=key1->first(), *e2=key2->first(), *new_tree=0;
  uint max_part_no= MY_MAX(key1->max_part_no, key2->max_part_no);

  while (e1 && e2)
  {
    int cmp=e1->cmp_min_to_min(e2);
    if (cmp < 0)
    {
      if (get_range(&e1,&e2,key1))
	continue;
    }
    else if (get_range(&e2,&e1,key2))
      continue;
    SEL_ARG *next=key_and(param, e1->next_key_part, e2->next_key_part,
                          clone_flag);
    e1->incr_refs();
    e2->incr_refs();
    if (!next || next->type != SEL_ARG::IMPOSSIBLE)
    {
      SEL_ARG *new_arg= e1->clone_and(param->thd, e2);
      if (!new_arg)
	return &null_element;			// End of memory
      new_arg->next_key_part=next;
      if (new_arg->next_key_part)
        new_arg->weight += new_arg->next_key_part->weight;

      if (!new_tree)
      {
	new_tree=new_arg;
      }
      else
	new_tree=new_tree->insert(new_arg);
    }
    if (e1->cmp_max_to_max(e2) < 0)
      e1=e1->next;				// e1 can't overlap next e2
    else
      e2=e2->next;
  }
  key1->free_tree();
  key2->free_tree();
  if (!new_tree)
    return &null_element;			// Impossible range
  new_tree->max_part_no= max_part_no;
  return new_tree;
}


static bool
get_range(SEL_ARG **e1,SEL_ARG **e2,SEL_ARG *root1)
{
  (*e1)=root1->find_range(*e2);			// first e1->min < e2->min
  if ((*e1)->cmp_max_to_min(*e2) < 0)
  {
    if (!((*e1)=(*e1)->next))
      return 1;
    if ((*e1)->cmp_min_to_max(*e2) > 0)
    {
      (*e2)=(*e2)->next;
      return 1;
    }
  }
  return 0;
}


#ifndef DBUG_OFF
/*
  Verify SEL_TREE's weight.

  Recompute the weight and compare
*/
uint SEL_ARG::verify_weight()
{
  uint computed_weight= 0;
  SEL_ARG *first_arg= first();

  if (first_arg)
  {
    for (SEL_ARG *arg= first_arg; arg; arg= arg->next)
    {
      computed_weight++;
      if (arg->next_key_part)
        computed_weight+= arg->next_key_part->verify_weight();
    }
  }
  else
  {
    // first()=NULL means this is a special kind of SEL_ARG, e.g.
    // SEL_ARG with type=MAYBE_KEY
    computed_weight= 1;
    if (next_key_part)
      computed_weight += next_key_part->verify_weight();
  }

  if (computed_weight != weight)
  {
    sql_print_error("SEL_ARG weight mismatch: computed %u have %u\n",
                    computed_weight, weight);
    DBUG_ASSERT(computed_weight == weight);  // Fail an assertion
  }
  return computed_weight;
}
#endif

static
SEL_ARG *key_or_with_limit(RANGE_OPT_PARAM *param, uint keyno,
                           SEL_ARG *key1, SEL_ARG *key2)
{
#ifndef DBUG_OFF
  if (key1)
    key1->verify_weight();
  if (key2)
    key2->verify_weight();
#endif

  SEL_ARG *res= key_or(param, key1, key2);
  res= enforce_sel_arg_weight_limit(param, keyno, res);
#ifndef DBUG_OFF
  if (res)
    res->verify_weight();
#endif
  return res;
}


static
SEL_ARG *key_and_with_limit(RANGE_OPT_PARAM *param, uint keyno,
                            SEL_ARG *key1, SEL_ARG *key2, uint clone_flag)
{
#ifndef DBUG_OFF
  if (key1)
    key1->verify_weight();
  if (key2)
    key2->verify_weight();
#endif
  SEL_ARG *res= key_and(param, key1, key2, clone_flag);
  res= enforce_sel_arg_weight_limit(param, keyno, res);
#ifndef DBUG_OFF
  if (res)
    res->verify_weight();
#endif
  return res;
}


/**
   Combine two range expression under a common OR. On a logical level, the
   transformation is key_or( expr1, expr2 ) => expr1 OR expr2.

   Both expressions are assumed to be in the SEL_ARG format. In a logic sense,
   the format is reminiscent of DNF, since an expression such as the following

   ( 1 < kp1 < 10 AND p1 ) OR ( 10 <= kp2 < 20 AND p2 )

   where there is a key consisting of keyparts ( kp1, kp2, ..., kpn ) and p1
   and p2 are valid SEL_ARG expressions over keyparts kp2 ... kpn, is a valid
   SEL_ARG condition. The disjuncts appear ordered by the minimum endpoint of
   the first range and ranges must not overlap. It follows that they are also
   ordered by maximum endpoints. Thus

   ( 1 < kp1 <= 2 AND ( kp2 = 2 OR kp2 = 3 ) ) OR kp1 = 3

   Is a valid SER_ARG expression for a key of at least 2 keyparts.
   
   For simplicity, we will assume that expr2 is a single range predicate,
   i.e. on the form ( a < x < b AND ... ). It is easy to generalize to a
   disjunction of several predicates by subsequently call key_or for each
   disjunct.

   The algorithm iterates over each disjunct of expr1, and for each disjunct
   where the first keypart's range overlaps with the first keypart's range in
   expr2:
   
   If the predicates are equal for the rest of the keyparts, or if there are
   no more, the range in expr2 has its endpoints copied in, and the SEL_ARG
   node in expr2 is deallocated. If more ranges became connected in expr1, the
   surplus is also deallocated. If they differ, two ranges are created.
   
   - The range leading up to the overlap. Empty if endpoints are equal.

   - The overlapping sub-range. May be the entire range if they are equal.

   Finally, there may be one more range if expr2's first keypart's range has a
   greater maximum endpoint than the last range in expr1.

   For the overlapping sub-range, we recursively call key_or. Thus in order to
   compute key_or of

     (1) ( 1 < kp1 < 10 AND 1 < kp2 < 10 ) 

     (2) ( 2 < kp1 < 20 AND 4 < kp2 < 20 )

   We create the ranges 1 < kp <= 2, 2 < kp1 < 10, 10 <= kp1 < 20. For the
   first one, we simply hook on the condition for the second keypart from (1)
   : 1 < kp2 < 10. For the second range 2 < kp1 < 10, key_or( 1 < kp2 < 10, 4
   < kp2 < 20 ) is called, yielding 1 < kp2 < 20. For the last range, we reuse
   the range 4 < kp2 < 20 from (2) for the second keypart. The result is thus
   
   ( 1  <  kp1 <= 2 AND 1 < kp2 < 10 ) OR
   ( 2  <  kp1 < 10 AND 1 < kp2 < 20 ) OR
   ( 10 <= kp1 < 20 AND 4 < kp2 < 20 )
*/
static SEL_ARG *
key_or(RANGE_OPT_PARAM *param, SEL_ARG *key1,SEL_ARG *key2)
{
  if (!key1)
  {
    if (key2)
    {
      key2->use_count--;
      key2->free_tree();
    }
    return 0;
  }
  if (!key2)
  {
    key1->use_count--;
    key1->free_tree();
    return 0;
  }
  key1->use_count--;
  key2->use_count--;

  if (key1->part != key2->part || 
      (key1->min_flag | key2->min_flag) & GEOM_FLAG)
  {
    key1->free_tree();
    key2->free_tree();
    return 0;                                   // Can't optimize this
  }

  // If one of the key is MAYBE_KEY then the found region may be bigger
  if (key1->type == SEL_ARG::MAYBE_KEY)
  {
    key2->free_tree();
    key1->use_count++;
    return key1;
  }
  if (key2->type == SEL_ARG::MAYBE_KEY)
  {
    key1->free_tree();
    key2->use_count++;
    return key2;
  }

  if (key1->use_count > 0)
  {
    if (key2->use_count == 0 || key1->elements > key2->elements)
    {
      swap_variables(SEL_ARG *,key1,key2);
    }
    if (key1->use_count > 0 && !(key1=key1->clone_tree(param)))
      return 0;                                 // OOM
  }

  // Add tree at key2 to tree at key1
  bool key2_shared=key2->use_count != 0;
  key1->maybe_flag|=key2->maybe_flag;

  /*
    Notation for illustrations used in the rest of this function: 

      Range: [--------]
             ^        ^
             start    stop

      Two overlapping ranges:
        [-----]               [----]            [--]
            [---]     or    [---]       or   [-------]

      Ambiguity: *** 
        The range starts or stops somewhere in the "***" range.
        Example: a starts before b and may end before/the same place/after b
        a: [----***]
        b:   [---]

      Adjacent ranges:
        Ranges that meet but do not overlap. Example: a = "x < 3", b = "x >= 3"
        a: ----]
        b:      [----
   */

  uint max_part_no= MY_MAX(key1->max_part_no, key2->max_part_no);

  for (key2=key2->first(); ; )
  {
    /*
      key1 consists of one or more ranges. tmp is the range currently
      being handled.

      initialize tmp to the latest range in key1 that starts the same
      place or before the range in key2 starts

      key2:           [------]
      key1: [---] [-----] [----]
                  ^
                  tmp
    */
    if (key1->min_flag & NO_MIN_RANGE &&
        key1->max_flag & NO_MAX_RANGE)
    {
      if (key1->maybe_flag)
        return new SEL_ARG(SEL_ARG::MAYBE_KEY);
      return 0;   // Always true OR
    }
    if (!key2)
      break;

    SEL_ARG *tmp=key1->find_range(key2);

    /*
      Used to describe how two key values are positioned compared to
      each other. Consider key_value_a.<cmp_func>(key_value_b):

        -2: key_value_a is smaller than key_value_b, and they are adjacent
        -1: key_value_a is smaller than key_value_b (not adjacent)
         0: the key values are equal
         1: key_value_a is bigger than key_value_b (not adjacent)
        -2: key_value_a is bigger than key_value_b, and they are adjacent

      Example: "cmp= tmp->cmp_max_to_min(key2)"

      key2:         [--------            (10 <= x ...)
      tmp:    -----]                      (... x <  10) => cmp==-2
      tmp:    ----]                       (... x <=  9) => cmp==-1
      tmp:    ------]                     (... x  = 10) => cmp== 0
      tmp:    --------]                   (... x <= 12) => cmp== 1
      (cmp == 2 does not make sense for cmp_max_to_min())
     */
    int cmp= 0;

    if (!tmp)
    {
      /*
        The range in key2 starts before the first range in key1. Use
        the first range in key1 as tmp.

        key2:     [--------]
        key1:            [****--] [----]   [-------]
                         ^
                         tmp
      */
      tmp=key1->first();
      cmp= -1;
    }
    else if ((cmp= tmp->cmp_max_to_min(key2)) < 0)
    {
      /*
        This is the case:
        key2:          [-------]
        tmp:   [----**]
       */
      SEL_ARG *next=tmp->next;
      if (cmp == -2 && eq_tree(tmp->next_key_part,key2->next_key_part))
      {
        /*
          Adjacent (cmp==-2) and equal next_key_parts => ranges can be merged

          This is the case:
          key2:          [-------]
          tmp:     [----]

          Result:
          key2:    [-------------]     => inserted into key1 below
          tmp:                         => deleted
        */
        SEL_ARG *key2_next=key2->next;
        if (key2_shared)
        {
          if (!(key2=new SEL_ARG(*key2)))
            return 0;           // out of memory
          key2->increment_use_count(key1->use_count+1);
          key2->next=key2_next;                 // New copy of key2
        }

        key2->copy_min(tmp);
        if (!(key1=key1->tree_delete(tmp)))
        {                                       // Only one key in tree
          if (key2->min_flag & NO_MIN_RANGE &&
              key2->max_flag & NO_MAX_RANGE)
          {
            if (key2->maybe_flag)
              return new SEL_ARG(SEL_ARG::MAYBE_KEY);
            return 0;   // Always true OR
          }
          key1=key2;
          key1->make_root();
          key2=key2_next;
          break;
        }
      }
      if (!(tmp=next)) // Move to next range in key1. Now tmp.min > key2.min
        break;         // No more ranges in key1. Copy rest of key2
    }

    if (cmp < 0)
    {
      /*
        This is the case:
        key2:  [--***]
        tmp:       [----]
      */
      int tmp_cmp;
      if ((tmp_cmp=tmp->cmp_min_to_max(key2)) > 0)
      {
        /*
          This is the case:
          key2:  [------**]
          tmp:             [----]
        */
        if (tmp_cmp == 2 && eq_tree(tmp->next_key_part,key2->next_key_part))
        {
          /*
            Adjacent ranges with equal next_key_part. Merge like this:

            This is the case:
            key2:    [------]
            tmp:             [-----]

            Result:
            key2:    [------]
            tmp:     [-------------]

            Then move on to next key2 range.
          */
          tmp->copy_min_to_min(key2);
          key1->merge_flags(key2);
          if (tmp->min_flag & NO_MIN_RANGE &&
              tmp->max_flag & NO_MAX_RANGE)
          {
            if (key1->maybe_flag)
              return new SEL_ARG(SEL_ARG::MAYBE_KEY);
            return 0;
          }
          key2->increment_use_count(-1);        // Free not used tree
          key2=key2->next;
          continue;
        }
        else
        {
          /*
            key2 not adjacent to tmp or has different next_key_part.
            Insert into key1 and move to next range in key2
            
            This is the case:
            key2:  [------**]
            tmp:             [----]

            Result:
            key1_  [------**][----]
                   ^         ^
                   insert    tmp
          */
          SEL_ARG *next=key2->next;
          if (key2_shared)
          {
            SEL_ARG *cpy= new SEL_ARG(*key2);   // Must make copy
            if (!cpy)
              return 0;                         // OOM
            key1=key1->insert(cpy);
            key2->increment_use_count(key1->use_count+1);
          }
          else
            key1=key1->insert(key2);            // Will destroy key2_root
          key2=next;
          continue;
        }
      }
    }

    /*
      The ranges in tmp and key2 are overlapping:

      key2:          [----------] 
      tmp:        [*****-----*****]

      Corollary: tmp.min <= key2.max
    */
    if (eq_tree(tmp->next_key_part,key2->next_key_part))
    {
      // Merge overlapping ranges with equal next_key_part
      if (tmp->is_same(key2))
      {
        /*
          Found exact match of key2 inside key1.
          Use the relevant range in key1.
        */
        tmp->merge_flags(key2);                 // Copy maybe flags
        key2->increment_use_count(-1);          // Free not used tree
      }
      else
      {
        SEL_ARG *last= tmp;
        SEL_ARG *first= tmp;

        /*
          Find the last range in key1 that overlaps key2 and
          where all ranges first...last have the same next_key_part as
          key2.

          key2:  [****----------------------*******]
          key1:     [--]  [----] [---]  [-----] [xxxx]
                    ^                   ^       ^
                    first               last    different next_key_part

          Since key2 covers them, the ranges between first and last
          are merged into one range by deleting first...last-1 from
          the key1 tree. In the figure, this applies to first and the
          two consecutive ranges. The range of last is then extended:
            * last.min: Set to MY_MIN(key2.min, first.min)
            * last.max: If there is a last->next that overlaps key2 (i.e.,
                        last->next has a different next_key_part):
                                        Set adjacent to last->next.min
                        Otherwise:      Set to MY_MAX(key2.max, last.max)

          Result:
          key2:  [****----------------------*******]
                    [--]  [----] [---]                   => deleted from key1
          key1:  [**------------------------***][xxxx]
                 ^                              ^
                 tmp=last                       different next_key_part
        */
        while (last->next && last->next->cmp_min_to_max(key2) <= 0 &&
               eq_tree(last->next->next_key_part,key2->next_key_part))
        {
          /*
            last->next is covered by key2 and has same next_key_part.
            last can be deleted
          */
          SEL_ARG *save=last;
          last=last->next;
          key1=key1->tree_delete(save);
        }
        // Redirect tmp to last which will cover the entire range
        tmp= last;

        /*
          We need the minimum endpoint of first so we can compare it
          with the minimum endpoint of the enclosing key2 range.
        */
        last->copy_min(first);
        bool full_range= last->copy_min(key2);
        if (!full_range)
        {
          if (last->next && key2->cmp_max_to_min(last->next) >= 0)
          {
            /*
              This is the case:
              key2:    [-------------]
              key1:  [***------]  [xxxx]
                     ^            ^
                     last         different next_key_part

              Extend range of last up to last->next:
              key2:    [-------------]
              key1:  [***--------][xxxx]
            */
            last->copy_min_to_max(last->next);
          }
          else
            /*
              This is the case:
              key2:    [--------*****]
              key1:  [***---------]    [xxxx]
                     ^                 ^
                     last              different next_key_part

              Extend range of last up to MY_MAX(last.max, key2.max):
              key2:    [--------*****]
              key1:  [***----------**] [xxxx]
             */
            full_range= last->copy_max(key2);
        }
        if (full_range)
        {                                       // Full range
          key1->free_tree();
          for (; key2 ; key2=key2->next)
            key2->increment_use_count(-1);      // Free not used tree
          if (key1->maybe_flag)
            return new SEL_ARG(SEL_ARG::MAYBE_KEY);
          return 0;
        }
      }
    }

    if (cmp >= 0 && tmp->cmp_min_to_min(key2) < 0)
    {
      /*
        This is the case ("cmp>=0" means that tmp.max >= key2.min):
        key2:              [----]
        tmp:     [------------*****]
      */

      if (!tmp->next_key_part)
      {
	SEL_ARG *key2_next= key2->next;
	if (key2_shared)
	{
	  SEL_ARG *key2_cpy= new SEL_ARG(*key2);
          if (!key2_cpy)
            return 0;
          key2= key2_cpy;
	}
        /*
          tmp->next_key_part is empty: cut the range that is covered
          by tmp from key2. 
          Reason: (key2->next_key_part OR tmp->next_key_part) will be
          empty and therefore equal to tmp->next_key_part. Thus, this
          part of the key2 range is completely covered by tmp.
        */
        if (tmp->cmp_max_to_max(key2) >= 0)
        {
          /*
            tmp covers the entire range in key2. 
            key2:              [----]
            tmp:     [-----------------]

            Move on to next range in key2
          */
          key2->increment_use_count(-1); // Free not used tree
          key2= key2_next;
        }
        else
        {
          /*
            This is the case:
            key2:           [-------]
            tmp:     [---------]

            Result:
            key2:               [---]
            tmp:     [---------]
          */
          key2->copy_max_to_min(tmp);
          key2->next= key2_next;                // In case of key2_shared
        }
        continue;
      }

      /*
        The ranges are overlapping but have not been merged because
        next_key_part of tmp and key2 differ. 
        key2:              [----]
        tmp:     [------------*****]

        Split tmp in two where key2 starts:
        key2:              [----]
        key1:    [--------][--*****]
                 ^         ^
                 insert    tmp
      */
      SEL_ARG *new_arg=tmp->clone_first(key2);
      if (!new_arg)
        return 0;                               // OOM
      if ((new_arg->next_key_part= tmp->next_key_part))
        new_arg->increment_use_count(key1->use_count+1);
      tmp->copy_min_to_min(key2);
      key1=key1->insert(new_arg);
    } // tmp.min >= key2.min due to this if()

    /*
      Now key2.min <= tmp.min <= key2.max:
      key2:   [---------]
      tmp:    [****---*****]
     */
    SEL_ARG key2_cpy(*key2); // Get copy we can modify
    for (;;)
    {
      if (tmp->cmp_min_to_min(&key2_cpy) > 0)
      {
        /*
          This is the case:
          key2_cpy:    [------------]
          key1:                 [-*****]
                                ^
                                tmp
                             
          Result:
          key2_cpy:             [---]
          key1:        [-------][-*****]
                       ^        ^
                       insert   tmp
         */
        SEL_ARG *new_arg=key2_cpy.clone_first(tmp);
        if (!new_arg)
          return 0; // OOM
        if ((new_arg->next_key_part=key2_cpy.next_key_part))
          new_arg->increment_use_count(key1->use_count+1);
        key1=key1->insert(new_arg);
        key2_cpy.copy_min_to_min(tmp);
      } 
      // Now key2_cpy.min == tmp.min

      if ((cmp= tmp->cmp_max_to_max(&key2_cpy)) <= 0)
      {
        /*
          tmp.max <= key2_cpy.max:
          key2_cpy:   a)  [-------]    or b)     [----]
          tmp:            [----]                 [----]

          Steps:
           1) Update next_key_part of tmp: OR it with key2_cpy->next_key_part.
           2) If case a: Insert range [tmp.max, key2_cpy.max] into key1 using
                         next_key_part of key2_cpy

           Result:
           key1:      a)  [----][-]    or b)     [----]
         */
        tmp->maybe_flag|= key2_cpy.maybe_flag;
        key2_cpy.increment_use_count(key1->use_count+1);

        uint old_weight= tmp->next_key_part? tmp->next_key_part->weight: 0;

        tmp->next_key_part= key_or(param, tmp->next_key_part,
                                   key2_cpy.next_key_part);

        uint new_weight= tmp->next_key_part? tmp->next_key_part->weight: 0;
        key1->weight += (new_weight - old_weight);

        if (!cmp)
          break;                     // case b: done with this key2 range

        // Make key2_cpy the range [tmp.max, key2_cpy.max]
        key2_cpy.copy_max_to_min(tmp);
        if (!(tmp=tmp->next))
        {
          /*
            No more ranges in key1. Insert key2_cpy and go to "end"
            label to insert remaining ranges in key2 if any.
          */
          SEL_ARG *tmp2= new SEL_ARG(key2_cpy);
          if (!tmp2)
            return 0; // OOM
          key1=key1->insert(tmp2);
          key2=key2->next;
          goto end;
        }
        if (tmp->cmp_min_to_max(&key2_cpy) > 0)
        {
          /*
            The next range in key1 does not overlap with key2_cpy.
            Insert this range into key1 and move on to the next range
            in key2.
          */
          SEL_ARG *tmp2= new SEL_ARG(key2_cpy);
          if (!tmp2)
            return 0;                           // OOM
          key1=key1->insert(tmp2);
          break;
        }
        /*
          key2_cpy overlaps with the next range in key1 and the case
          is now "key2.min <= tmp.min <= key2.max". Go back to for(;;)
          to handle this situation.
        */
        continue;
      }
      else
      {
        /*
          This is the case:
          key2_cpy:   [-------]
          tmp:        [------------]

          Result:
          key1:       [-------][---]
                      ^        ^
                      new_arg  tmp
          Steps:
           0) If tmp->next_key_part is empty: do nothing. Reason:
              (key2_cpy->next_key_part OR tmp->next_key_part) will be
              empty and therefore equal to tmp->next_key_part. Thus,
              the range in key2_cpy is completely covered by tmp
           1) Make new_arg with range [tmp.min, key2_cpy.max].
              new_arg->next_key_part is OR between next_key_part
              of tmp and key2_cpy
           2) Make tmp the range [key2.max, tmp.max]
           3) Insert new_arg into key1
        */
        if (!tmp->next_key_part) // Step 0
        {
          key2_cpy.increment_use_count(-1);     // Free not used tree
          break;
        }
        SEL_ARG *new_arg=tmp->clone_last(&key2_cpy);
        if (!new_arg)
          return 0; // OOM
        tmp->copy_max_to_min(&key2_cpy);
        tmp->increment_use_count(key1->use_count+1);
        /* Increment key count as it may be used for next loop */
        key2_cpy.increment_use_count(1);
        new_arg->next_key_part= key_or(param, tmp->next_key_part,
                                       key2_cpy.next_key_part);
        key1=key1->insert(new_arg);
        break;
      }
    }
    // Move on to next range in key2
    key2=key2->next;                            
  }

end:
  /*
    Add key2 ranges that are non-overlapping with and higher than the
    highest range in key1.
  */
  while (key2)
  {
    SEL_ARG *next=key2->next;
    if (key2_shared)
    {
      SEL_ARG *tmp=new SEL_ARG(*key2);          // Must make copy
      if (!tmp)
        return 0;
      key2->increment_use_count(key1->use_count+1);
      key1=key1->insert(tmp);
    }
    else
      key1=key1->insert(key2);                  // Will destroy key2_root
    key2=next;
  }
  key1->use_count++;

  key1->max_part_no= max_part_no;
  return key1;
}


/* Compare if two trees are equal */

static bool eq_tree(SEL_ARG* a,SEL_ARG *b)
{
  if (a == b)
    return 1;
  if (!a || !b || !a->is_same(b))
    return 0;
  if (a->left != &null_element && b->left != &null_element)
  {
    if (!eq_tree(a->left,b->left))
      return 0;
  }
  else if (a->left != &null_element || b->left != &null_element)
    return 0;
  if (a->right != &null_element && b->right != &null_element)
  {
    if (!eq_tree(a->right,b->right))
      return 0;
  }
  else if (a->right != &null_element || b->right != &null_element)
    return 0;
  if (a->next_key_part != b->next_key_part)
  {						// Sub range
    if (!a->next_key_part != !b->next_key_part ||
	!eq_tree(a->next_key_part, b->next_key_part))
      return 0;
  }
  return 1;
}


/*
  Compute the MAX(key part) in this SEL_ARG graph.
*/
uint SEL_ARG::get_max_key_part() const
{
  const SEL_ARG *cur;
  uint max_part= part;
  for (cur= first(); cur ; cur=cur->next)
  {
    if (cur->next_key_part)
    {
      uint mp= cur->next_key_part->get_max_key_part();
      max_part= MY_MAX(part, mp);
    }
  }
  return max_part;
}


/**
  Compute the number of eq_ranges top elements in the tree

  This is used by the cost_group_min_max() to calculate the number of
  groups in SEL_TREE

  @param group_key_parts number of key parts that must be equal

  @return < 0  Not known
  @return >= 0  Number of groups
*/

int SEL_ARG::number_of_eq_groups(uint group_key_parts) const
{
  int elements= 0;
  SEL_ARG const *cur;

  if (part > group_key_parts-1 || type != KEY_RANGE)
    return -1;

  cur= first();
  do
  {
    if ((cur->min_flag | cur->max_flag) &
        (NO_MIN_RANGE | NO_MAX_RANGE | NEAR_MIN | NEAR_MAX | GEOM_FLAG))
      return -1;
    if (min_value != max_value && !min_max_are_equal())
      return -1;
    if (part != group_key_parts -1)
    {
      int tmp;
      if (!next_key_part)
        return -1;
      if ((tmp= next_key_part->number_of_eq_groups(group_key_parts)) < 0)
        return -1;
      elements+= tmp;
    }
    else
      elements++;
  } while ((cur= cur->next));
  return elements;
}


/*
  Remove the SEL_ARG graph elements which have part > max_part.

  @detail
    Also update weight for the graph and any modified subgraphs.
*/

void prune_sel_arg_graph(SEL_ARG *sel_arg, uint max_part)
{
  SEL_ARG *cur;
  DBUG_ASSERT(max_part >= sel_arg->part);

  for (cur= sel_arg->first(); cur ; cur=cur->next)
  {
    if (cur->next_key_part)
    {
      if (cur->next_key_part->part > max_part)
      {
        // Remove cur->next_key_part.
        sel_arg->weight -= cur->next_key_part->weight;
        cur->next_key_part= NULL;
      }
      else
      {
        uint old_weight= cur->next_key_part->weight;
        prune_sel_arg_graph(cur->next_key_part, max_part);
        sel_arg->weight -= (old_weight - cur->next_key_part->weight);
      }
    }
  }
}


/*
  @brief
    Make sure the passed SEL_ARG graph's weight is below SEL_ARG::MAX_WEIGHT,
    by cutting off branches if necessary.

  @detail
    @see declaration of SEL_ARG::weight for definition of weight.

    This function attempts to reduce the graph's weight by cutting off
    SEL_ARG::next_key_part connections if necessary.

    We start with maximum used keypart and then remove one keypart after
    another until the graph's weight is within the limit.

  @seealso
     sel_arg_and_weight_heuristic();

  @return
    tree pointer  The tree after processing,
    NULL          If it was not possible to reduce the weight of the tree below
                  the limit.
*/

SEL_ARG *enforce_sel_arg_weight_limit(RANGE_OPT_PARAM *param, uint keyno,
                                      SEL_ARG *sel_arg)
{
  if (!sel_arg || sel_arg->type != SEL_ARG::KEY_RANGE ||
      !param->thd->variables.optimizer_max_sel_arg_weight)
    return sel_arg;

  Field *field= sel_arg->field;
  uint weight1= sel_arg->weight;

  while (1)
  {
    if (likely(sel_arg->weight <= param->thd->variables.
                                  optimizer_max_sel_arg_weight))
      break;

    uint max_part= sel_arg->get_max_key_part();
    if (max_part == sel_arg->part)
    {
      /*
        We don't return NULL right away as we want to have the information
        about the changed tree in the optimizer trace.
      */
      sel_arg= NULL;
      break;
    }

    max_part--;
    prune_sel_arg_graph(sel_arg, max_part);
  }

  uint weight2= sel_arg? sel_arg->weight : 0;

  if (unlikely(weight2 != weight1 && param->thd->trace_started()))
  {
    Json_writer_object wrapper(param->thd);
    Json_writer_object obj(param->thd, "enforce_sel_arg_weight_limit");
    if (param->using_real_indexes)
      obj.add("index", param->table->key_info[param->real_keynr[keyno]].name);
    else
      obj.add("pseudo_index", field->field_name);

    obj.
      add("old_weight", (longlong)weight1).
      add("new_weight", (longlong)weight2);
  }
  return sel_arg;
}


/*
  @detail
    Do not combine the trees if their total weight is likely to exceed the
    MAX_WEIGHT.
    (It is possible that key1 has next_key_part that has empty overlap with
    key2. In this case, the combined tree will have a smaller weight than we
    predict. We assume this is rare.)
*/

static
bool sel_arg_and_weight_heuristic(RANGE_OPT_PARAM *param, SEL_ARG *key1,
                                  SEL_ARG *key2)
{
  DBUG_ASSERT(key1->part < key2->part);

  ulong max_weight= param->thd->variables.optimizer_max_sel_arg_weight;
  if (max_weight && key1->weight + key1->elements*key2->weight > max_weight)
  {
    if (unlikely(param->thd->trace_started()))
    {
      Json_writer_object wrapper(param->thd);
      Json_writer_object obj(param->thd, "sel_arg_weight_heuristic");

      if (key1->type == SEL_ARG::KEY_RANGE)
        obj.add("key1_field", key1->field->field_name);
      else
        obj.add("key1_type", (uint) key1->type);

      if (key2->type == SEL_ARG::KEY_RANGE)
        obj.add("key2_field", key2->field->field_name);
      else
        obj.add("key2_type", (uint) key2->type);

      obj.add("key1_weight", (longlong) key1->weight);
      obj.add("key2_weight", (longlong) key2->weight);
    }
    return true; // Discard key2
  }
  return false;
}


SEL_ARG *
SEL_ARG::insert(SEL_ARG *key)
{
  SEL_ARG *element,**UNINIT_VAR(par),*UNINIT_VAR(last_element);

  for (element= this; element != &null_element ; )
  {
    last_element=element;
    if (key->cmp_min_to_min(element) > 0)
    {
      par= &element->right; element= element->right;
    }
    else
    {
      par = &element->left; element= element->left;
    }
  }
  *par=key;
  key->parent=last_element;
	/* Link in list */
  if (par == &last_element->left)
  {
    key->next=last_element;
    if ((key->prev=last_element->prev))
      key->prev->next=key;
    last_element->prev=key;
  }
  else
  {
    if ((key->next=last_element->next))
      key->next->prev=key;
    key->prev=last_element;
    last_element->next=key;
  }
  key->left=key->right= &null_element;
  SEL_ARG *root=rb_insert(key);			// rebalance tree
  root->use_count=this->use_count;		// copy root info
  root->elements= this->elements+1;
  /*
    The new weight is:
     old root's weight
     +1 for the weight of the added element
     + next_key_part's weight of the added element
  */
  root->weight = weight + 1 + (key->next_key_part? key->next_key_part->weight: 0);
  root->maybe_flag=this->maybe_flag;
  return root;
}


/*
** Find best key with min <= given key
** Because the call context this should never return 0 to get_range
*/

SEL_ARG *
SEL_ARG::find_range(SEL_ARG *key)
{
  SEL_ARG *element=this,*found=0;

  for (;;)
  {
    if (element == &null_element)
      return found;
    int cmp=element->cmp_min_to_min(key);
    if (cmp == 0)
      return element;
    if (cmp < 0)
    {
      found=element;
      element=element->right;
    }
    else
      element=element->left;
  }
}


/*
  Remove a element from the tree

  SYNOPSIS
    tree_delete()
    key		Key that is to be deleted from tree (this)

  NOTE
    This also frees all sub trees that is used by the element

  RETURN
    root of new tree (with key deleted)
*/

SEL_ARG *
SEL_ARG::tree_delete(SEL_ARG *key)
{
  enum leaf_color remove_color;
  SEL_ARG *root,*nod,**par,*fix_par;
  DBUG_ENTER("tree_delete");

  root=this;
  this->parent= 0;

  /*
    Compute the weight the tree will have after the element is removed.
    We remove the element itself (weight=1)
    and the sub-graph connected to its next_key_part.
  */
  uint new_weight= root->weight - (1 + (key->next_key_part?
                                        key->next_key_part->weight : 0));

  DBUG_ASSERT(root->weight >= (1 + (key->next_key_part ?
                                    key->next_key_part->weight : 0)));

  /* Unlink from list */
  if (key->prev)
    key->prev->next=key->next;
  if (key->next)
    key->next->prev=key->prev;
  key->increment_use_count(-1);
  if (!key->parent)
    par= &root;
  else
    par=key->parent_ptr();

  if (key->left == &null_element)
  {
    *par=nod=key->right;
    fix_par=key->parent;
    if (nod != &null_element)
      nod->parent=fix_par;
    remove_color= key->color;
  }
  else if (key->right == &null_element)
  {
    *par= nod=key->left;
    nod->parent=fix_par=key->parent;
    remove_color= key->color;
  }
  else
  {
    SEL_ARG *tmp=key->next;			// next bigger key (exist!)
    nod= *tmp->parent_ptr()= tmp->right;	// unlink tmp from tree
    fix_par=tmp->parent;
    if (nod != &null_element)
      nod->parent=fix_par;
    remove_color= tmp->color;

    tmp->parent=key->parent;			// Move node in place of key
    (tmp->left=key->left)->parent=tmp;
    if ((tmp->right=key->right) != &null_element)
      tmp->right->parent=tmp;
    tmp->color=key->color;
    *par=tmp;
    if (fix_par == key)				// key->right == key->next
      fix_par=tmp;				// new parent of nod
  }

  if (root == &null_element)
    DBUG_RETURN(0);				// Maybe root later
  if (remove_color == BLACK)
    root=rb_delete_fixup(root,nod,fix_par);
  test_rb_tree(root,root->parent);

  root->use_count=this->use_count;		// Fix root counters
  root->weight= new_weight;
  root->elements=this->elements-1;
  root->maybe_flag=this->maybe_flag;
  DBUG_RETURN(root);
}


	/* Functions to fix up the tree after insert and delete */

static void left_rotate(SEL_ARG **root,SEL_ARG *leaf)
{
  SEL_ARG *y=leaf->right;
  leaf->right=y->left;
  if (y->left != &null_element)
    y->left->parent=leaf;
  if (!(y->parent=leaf->parent))
    *root=y;
  else
    *leaf->parent_ptr()=y;
  y->left=leaf;
  leaf->parent=y;
}

static void right_rotate(SEL_ARG **root,SEL_ARG *leaf)
{
  SEL_ARG *y=leaf->left;
  leaf->left=y->right;
  if (y->right != &null_element)
    y->right->parent=leaf;
  if (!(y->parent=leaf->parent))
    *root=y;
  else
    *leaf->parent_ptr()=y;
  y->right=leaf;
  leaf->parent=y;
}


SEL_ARG *
SEL_ARG::rb_insert(SEL_ARG *leaf)
{
  SEL_ARG *y,*par,*par2,*root;
  root= this; root->parent= 0;

  leaf->color=RED;
  while (leaf != root && (par= leaf->parent)->color == RED)
  {					// This can't be root or 1 level under
    if (par == (par2= leaf->parent->parent)->left)
    {
      y= par2->right;
      if (y->color == RED)
      {
	par->color=BLACK;
	y->color=BLACK;
	leaf=par2;
	leaf->color=RED;		/* And the loop continues */
      }
      else
      {
	if (leaf == par->right)
	{
	  left_rotate(&root,leaf->parent);
	  par=leaf;			/* leaf is now parent to old leaf */
	}
	par->color=BLACK;
	par2->color=RED;
	right_rotate(&root,par2);
	break;
      }
    }
    else
    {
      y= par2->left;
      if (y->color == RED)
      {
	par->color=BLACK;
	y->color=BLACK;
	leaf=par2;
	leaf->color=RED;		/* And the loop continues */
      }
      else
      {
	if (leaf == par->left)
	{
	  right_rotate(&root,par);
	  par=leaf;
	}
	par->color=BLACK;
	par2->color=RED;
	left_rotate(&root,par2);
	break;
      }
    }
  }
  root->color=BLACK;
  test_rb_tree(root,root->parent);
  return root;
}


SEL_ARG *rb_delete_fixup(SEL_ARG *root,SEL_ARG *key,SEL_ARG *par)
{
  SEL_ARG *x,*w;
  root->parent=0;

  x= key;
  while (x != root && x->color == SEL_ARG::BLACK)
  {
    if (x == par->left)
    {
      w=par->right;
      if (w->color == SEL_ARG::RED)
      {
	w->color=SEL_ARG::BLACK;
	par->color=SEL_ARG::RED;
	left_rotate(&root,par);
	w=par->right;
      }
      if (w->left->color == SEL_ARG::BLACK && w->right->color == SEL_ARG::BLACK)
      {
	w->color=SEL_ARG::RED;
	x=par;
      }
      else
      {
	if (w->right->color == SEL_ARG::BLACK)
	{
	  w->left->color=SEL_ARG::BLACK;
	  w->color=SEL_ARG::RED;
	  right_rotate(&root,w);
	  w=par->right;
	}
	w->color=par->color;
	par->color=SEL_ARG::BLACK;
	w->right->color=SEL_ARG::BLACK;
	left_rotate(&root,par);
	x=root;
	break;
      }
    }
    else
    {
      w=par->left;
      if (w->color == SEL_ARG::RED)
      {
	w->color=SEL_ARG::BLACK;
	par->color=SEL_ARG::RED;
	right_rotate(&root,par);
	w=par->left;
      }
      if (w->right->color == SEL_ARG::BLACK && w->left->color == SEL_ARG::BLACK)
      {
	w->color=SEL_ARG::RED;
	x=par;
      }
      else
      {
	if (w->left->color == SEL_ARG::BLACK)
	{
	  w->right->color=SEL_ARG::BLACK;
	  w->color=SEL_ARG::RED;
	  left_rotate(&root,w);
	  w=par->left;
	}
	w->color=par->color;
	par->color=SEL_ARG::BLACK;
	w->left->color=SEL_ARG::BLACK;
	right_rotate(&root,par);
	x=root;
	break;
      }
    }
    par=x->parent;
  }
  x->color=SEL_ARG::BLACK;
  return root;
}


	/* Test that the properties for a red-black tree hold */

#ifdef EXTRA_DEBUG
int test_rb_tree(SEL_ARG *element,SEL_ARG *parent)
{
  int count_l,count_r;

  if (element == &null_element)
    return 0;					// Found end of tree
  if (element->parent != parent)
  {
    sql_print_error("Wrong tree: Parent doesn't point at parent");
    return -1;
  }
  if (element->color == SEL_ARG::RED &&
      (element->left->color == SEL_ARG::RED ||
       element->right->color == SEL_ARG::RED))
  {
    sql_print_error("Wrong tree: Found two red in a row");
    return -1;
  }
  if (element->left == element->right && element->left != &null_element)
  {						// Dummy test
    sql_print_error("Wrong tree: Found right == left");
    return -1;
  }
  count_l=test_rb_tree(element->left,element);
  count_r=test_rb_tree(element->right,element);
  if (count_l >= 0 && count_r >= 0)
  {
    if (count_l == count_r)
      return count_l+(element->color == SEL_ARG::BLACK);
    sql_print_error("Wrong tree: Incorrect black-count: %d - %d",
	    count_l,count_r);
  }
  return -1;					// Error, no more warnings
}


/**
  Count how many times SEL_ARG graph "root" refers to its part "key" via
  transitive closure.
  
  @param root  An RB-Root node in a SEL_ARG graph.
  @param key   Another RB-Root node in that SEL_ARG graph.

  The passed "root" node may refer to "key" node via root->next_key_part,
  root->next->n

  This function counts how many times the node "key" is referred (via
  SEL_ARG::next_key_part) by 
  - intervals of RB-tree pointed by "root", 
  - intervals of RB-trees that are pointed by SEL_ARG::next_key_part from 
  intervals of RB-tree pointed by "root",
  - and so on.
    
  Here is an example (horizontal links represent next_key_part pointers, 
  vertical links - next/prev prev pointers):  
    
         +----+               $
         |root|-----------------+
         +----+               $ |
           |                  $ |
           |                  $ |
         +----+       +---+   $ |     +---+    Here the return value
         |    |- ... -|   |---$-+--+->|key|    will be 4.
         +----+       +---+   $ |  |  +---+
           |                  $ |  |
          ...                 $ |  |
           |                  $ |  |
         +----+   +---+       $ |  |
         |    |---|   |---------+  |
         +----+   +---+       $    |
           |        |         $    |
          ...     +---+       $    |
                  |   |------------+
                  +---+       $
  @return 
  Number of links to "key" from nodes reachable from "root".
*/

static ulong count_key_part_usage(SEL_ARG *root, SEL_ARG *key)
{
  ulong count= 0;
  for (root=root->first(); root ; root=root->next)
  {
    if (root->next_key_part)
    {
      if (root->next_key_part == key)
	count++;
      if (root->next_key_part->part < key->part)
	count+=count_key_part_usage(root->next_key_part,key);
    }
  }
  return count;
}


/*
  Check if SEL_ARG::use_count value is correct

  SYNOPSIS
    SEL_ARG::test_use_count()
      root  The root node of the SEL_ARG graph (an RB-tree root node that
            has the least value of sel_arg->part in the entire graph, and
            thus is the "origin" of the graph)

  DESCRIPTION
    Check if SEL_ARG::use_count value is correct. See the definition of
    use_count for what is "correct".
*/

void SEL_ARG::test_use_count(SEL_ARG *root)
{
  uint e_count=0;

  if (this->type != SEL_ARG::KEY_RANGE)
    return;
  for (SEL_ARG *pos=first(); pos ; pos=pos->next)
  {
    e_count++;
    if (pos->next_key_part)
    {
      ulong count=count_key_part_usage(root,pos->next_key_part);
      if (count > pos->next_key_part->use_count)
      {
        sql_print_information("Use_count: Wrong count for key at %p: %lu "
                              "should be %lu", pos,
                              pos->next_key_part->use_count, count);
	return;
      }
      pos->next_key_part->test_use_count(root);
    }
  }
  if (e_count != elements)
    sql_print_warning("Wrong use count: %u (should be %u) for tree at %p",
                      e_count, elements, this);
}
#endif


/**
  Check if first key part has only one value

  @retval 1 yes
  @retval 0 no
*/

static bool check_if_first_key_part_has_only_one_value(SEL_ARG *arg)
{
  if (arg->left != &null_element || arg->right != &null_element)
    return 0;                                    // Multiple key values
  if ((arg->min_flag | arg->max_flag) & (NEAR_MIN | NEAR_MAX))
    return 0;
  if (unlikely(arg->type != SEL_ARG::KEY_RANGE)) // Not a valid range
    return 0;
  return arg->min_value == arg->max_value || !arg->cmp_min_to_max(arg);
}


/*
  Calculate cost and E(#rows) for a given index and intervals tree 

  SYNOPSIS
    check_quick_select()
      param             Parameter from test_quick_select
      idx               Number of index to use in PARAM::key SEL_TREE::key
      index_only        TRUE  - assume only index tuples will be accessed
                        FALSE - assume full table rows will be read
      tree              Transformed selection condition, tree->key[idx] holds
                        the intervals for the given index.
      update_tbl_stats  TRUE <=> update table->quick_* with information
                        about range scan we've evaluated.
      mrr_flags   INOUT MRR access flags
      cost        OUT   Scan cost
      is_ror_scan       is set to reflect if the key scan is a ROR (see
                        is_key_scan_ror function for more info)

  NOTES
    param->table->opt_range*, param->range_count (and maybe others) are
    updated with data of given key scan, see quick_range_seq_next for details.

  RETURN
    Estimate # of records to be retrieved.
    HA_POS_ERROR if estimate calculation failed due to table handler problems.
*/

static
ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
                           bool index_only,
                           SEL_ARG *tree, bool update_tbl_stats, 
                           uint *mrr_flags, uint *bufsize, Cost_estimate *cost,
                           bool *is_ror_scan)
{
  SEL_ARG_RANGE_SEQ seq;
  RANGE_SEQ_IF seq_if=
    {NULL, sel_arg_range_seq_init, sel_arg_range_seq_next, 0, 0};
  handler *file= param->table->file;
  ha_rows rows= HA_POS_ERROR;
  uint keynr= param->real_keynr[idx];
  DBUG_ENTER("check_quick_select");

  /* Range not calculated yet */
  param->quick_rows[keynr]= HA_POS_ERROR;

  /* Handle cases when we don't have a valid non-empty list of range */
  if (!tree)
    DBUG_RETURN(HA_POS_ERROR);
  if (tree->type == SEL_ARG::IMPOSSIBLE)
    DBUG_RETURN(0L);
  if (tree->type != SEL_ARG::KEY_RANGE || tree->part != 0)
    DBUG_RETURN(HA_POS_ERROR);

  seq.keyno= idx;
  seq.real_keyno= keynr;
  seq.key_parts= param->key[idx];
  seq.param= param;
  seq.start= tree;

  param->range_count=0;
  param->max_key_parts=0;

  seq.is_ror_scan= TRUE;
  if (param->table->key_info[keynr].index_flags & HA_KEY_SCAN_NOT_ROR)
    seq.is_ror_scan= FALSE;
  
  *mrr_flags= param->force_default_mrr? HA_MRR_USE_DEFAULT_IMPL: 0;
  /*
    Pass HA_MRR_SORTED to see if MRR implementation can handle sorting.
  */
  *mrr_flags|= HA_MRR_NO_ASSOCIATION | HA_MRR_SORTED;

  // TODO: param->max_key_parts holds 0 now, and not the #keyparts used.
  // Passing wrong second argument to index_flags() makes no difference for
  // most storage engines but might be an issue for MyRocks with certain
  // datatypes.
  // Note that HA_KEYREAD_ONLY implies that this is not a clustered index
  if (index_only && 
      (file->index_flags(keynr, param->max_key_parts, 1) & HA_KEYREAD_ONLY))
     *mrr_flags |= HA_MRR_INDEX_ONLY;
  
  if (param->thd->lex->sql_command != SQLCOM_SELECT)
    *mrr_flags |= HA_MRR_USE_DEFAULT_IMPL;

  *bufsize= param->thd->variables.mrr_buff_size;
  /*
    Skip materialized derived table/view result table from MRR check as
    they aren't contain any data yet.
  */
  if (!param->table->pos_in_table_list->is_materialized_derived())
    rows= file->multi_range_read_info_const(keynr, &seq_if, (void*)&seq, 0,
                                            bufsize, mrr_flags, limit, cost);
  param->quick_rows[keynr]= rows;
  if (rows != HA_POS_ERROR)
  {
    ha_rows table_records= param->table->stat_records();
    if (rows > table_records)
    {
      ha_rows diff= rows - table_records;
      /*
        For any index the total number of records within all ranges
        cannot be bigger than the number of records in the table.
        This check is needed as sometimes that table statistics or range
        estimates may be slightly out of sync.

        We cannot do this easily in the above multi_range_read_info_const()
        call as then we would need to have similar adjustments done
        in the partitioning engine.
      */
      rows= MY_MAX(table_records, 1);
      param->quick_rows[keynr]= rows;
      /* Adjust costs */
      cost->comp_cost-= file->WHERE_COST * diff;
    }
    param->possible_keys.set_bit(keynr);
    if (update_tbl_stats)
    {
      TABLE::OPT_RANGE *range= param->table->opt_range + keynr;
      param->table->opt_range_keys.set_bit(keynr);
      range->key_parts= param->max_key_parts;
      range->ranges= param->range_count;
      param->table->set_opt_range_condition_rows(rows);
      range->selectivity= (rows ?
                           (param->table->opt_range_condition_rows /
                            rows) :
                           1.0);                // ok as rows is 0
      range->rows= rows;
      range->cost= *cost;
      range->max_index_blocks= file->index_blocks(keynr, range->ranges,
                                                  rows);
      range->max_row_blocks= MY_MIN(file->row_blocks(), rows * file->stats.block_size / IO_SIZE);
      range->first_key_part_has_only_one_value=
        check_if_first_key_part_has_only_one_value(tree);
    }
  }

  /* Figure out if the key scan is ROR (returns rows in ROWID order) or not */
  enum ha_key_alg key_alg= param->table->key_info[seq.real_keyno].algorithm;
  if ((key_alg != HA_KEY_ALG_BTREE) && (key_alg!= HA_KEY_ALG_UNDEF))
  {
    /* 
      All scans are non-ROR scans for those index types.
      TODO: Don't have this logic here, make table engines return 
      appropriate flags instead.
    */
    seq.is_ror_scan= FALSE;
  }
  else if (param->table->file->is_clustering_key(keynr))
  {
    /* Clustered PK scan is always a ROR scan (TODO: same as above) */
    seq.is_ror_scan= TRUE;
  }
  else if (param->range_count > 1)
  {
    /* 
      Scanning multiple key values in the index: the records are ROR
      for each value, but not between values. E.g, "SELECT ... x IN
      (1,3)" returns ROR order for all records with x=1, then ROR
      order for records with x=3
    */
    seq.is_ror_scan= FALSE;
  }
  *is_ror_scan= seq.is_ror_scan;

  DBUG_PRINT("exit", ("Records: %lu", (ulong) rows));
  DBUG_ASSERT(rows == HA_POS_ERROR ||
              rows <= MY_MAX(param->table->stat_records(), 1));
  DBUG_RETURN(rows); //psergey-merge:todo: maintain first_null_comp.
}


/*
  Check if key scan on given index with equality conditions on first n key
  parts is a ROR scan.

  SYNOPSIS
    is_key_scan_ror()
      param  Parameter from test_quick_select
      keynr  Number of key in the table. The key must not be a clustered
             primary key.
      nparts Number of first key parts for which equality conditions
             are present.

  NOTES
    ROR (Rowid Ordered Retrieval) key scan is a key scan that produces
    ordered sequence of rowids (ha_xxx::cmp_ref is the comparison function)

    This function is needed to handle a practically-important special case:
    an index scan is a ROR scan if it is done using a condition in form

        "key1_1=c_1 AND ... AND key1_n=c_n"

    where the index is defined on (key1_1, ..., key1_N [,a_1, ..., a_n])

    and the table has a clustered Primary Key defined as 
      PRIMARY KEY(a_1, ..., a_n, b1, ..., b_k) 
    
    i.e. the first key parts of it are identical to uncovered parts ot the 
    key being scanned. This function assumes that the index flags do not
    include HA_KEY_SCAN_NOT_ROR flag (that is checked elsewhere).

    Check (1) is made in quick_range_seq_next()

  RETURN
    TRUE   The scan is ROR-scan
    FALSE  Otherwise
*/

static bool is_key_scan_ror(PARAM *param, uint keynr, uint8 nparts)
{
  KEY *table_key= param->table->key_info + keynr;
  KEY_PART_INFO *key_part= table_key->key_part + nparts;
  KEY_PART_INFO *key_part_end= (table_key->key_part +
                                table_key->user_defined_key_parts);
  uint pk_number;
  
  if (param->table->file->ha_table_flags() & HA_NON_COMPARABLE_ROWID)
    return false;

  for (KEY_PART_INFO *kp= table_key->key_part; kp < key_part; kp++)
  {
    field_index_t fieldnr= (param->table->key_info[keynr].
                            key_part[kp - table_key->key_part].fieldnr - 1);
    if (param->table->field[fieldnr]->key_length() != kp->length)
      return FALSE;
  }
  
  if (key_part >= key_part_end)
    return TRUE;

  pk_number= param->table->s->primary_key;
  if (!param->table->file->pk_is_clustering_key(pk_number))
    return FALSE;

  if (keynr == pk_number)
    return TRUE; /* Scan on clustered PK is always ROR */


  KEY_PART_INFO *pk_part= param->table->key_info[pk_number].key_part;
  KEY_PART_INFO *pk_part_end= pk_part +
                              param->table->key_info[pk_number].user_defined_key_parts;
  /*
    Check for columns indexed with DESC.
    If a column is present in both Secondary Key and Primary Key and either of
    indexes include it with DESC, then the scan is not a ROR scan.
  */
  for (; key_part != key_part_end; ++key_part)
  {
    pk_part= param->table->key_info[pk_number].key_part;
    for (; pk_part != pk_part_end; ++pk_part)
    {
      if (key_part->fieldnr == pk_part->fieldnr &&
          (MY_TEST(key_part->key_part_flag & HA_REVERSE_SORT) ||
           MY_TEST(pk_part->key_part_flag & HA_REVERSE_SORT)))
        return FALSE;
    }
  }

  /*
    If there are equalities for all key parts, it is a ROR scan. If there are
    equalities all keyparts and even some of key parts from "Extended Key"
    index suffix, it is a ROR-scan, too.
  */
  key_part= table_key->key_part + nparts;
  pk_part= param->table->key_info[pk_number].key_part;
  for (;(key_part!=key_part_end) && (pk_part != pk_part_end);
       ++key_part, ++pk_part)
  {
    if ((key_part->field != pk_part->field) ||
        (key_part->length != pk_part->length))
      return FALSE;
  }
  return (key_part == key_part_end);
}


/*
  Create a QUICK_RANGE_SELECT from given key and SEL_ARG tree for that key.

  SYNOPSIS
    get_quick_select()
      param
      idx            Index of used key in param->key.
      key_tree       SEL_ARG tree for the used key
      mrr_flags      MRR parameter for quick select
      mrr_buf_size   MRR parameter for quick select
      parent_alloc   If not NULL, use it to allocate memory for
                     quick select data. Otherwise use quick->alloc.
  NOTES
    The caller must call QUICK_SELECT::init for returned quick select.

    CAUTION! This function may change thd->mem_root to a MEM_ROOT which will be
    deallocated when the returned quick select is deleted.

  RETURN
    NULL on error
    otherwise created quick select
*/

QUICK_RANGE_SELECT *
get_quick_select(PARAM *param,uint idx,SEL_ARG *key_tree, uint mrr_flags,
                 uint mrr_buf_size, MEM_ROOT *parent_alloc)
{
  QUICK_RANGE_SELECT *quick;
  bool create_err= FALSE;
  DBUG_ENTER("get_quick_select");

  if (param->table->key_info[param->real_keynr[idx]].algorithm == HA_KEY_ALG_RTREE)
    quick=new QUICK_RANGE_SELECT_GEOM(param->thd, param->table,
                                      param->real_keynr[idx],
                                      MY_TEST(parent_alloc),
                                      parent_alloc, &create_err);
  else
    quick=new QUICK_RANGE_SELECT(param->thd, param->table,
                                 param->real_keynr[idx],
                                 MY_TEST(parent_alloc), NULL, &create_err);

  if (quick)
  {
    if (create_err ||
	get_quick_keys(param,quick,param->key[idx],key_tree,param->min_key,0,
		       param->max_key,0))
    {
      delete quick;
      quick=0;
    }
    else
    {
      KEY *keyinfo= param->table->key_info+param->real_keynr[idx];
      quick->mrr_flags= mrr_flags;
      quick->mrr_buf_size= mrr_buf_size;
      quick->key_parts=(KEY_PART*)
        memdup_root(parent_alloc? parent_alloc : &quick->alloc,
                    (char*) param->key[idx],
                    sizeof(KEY_PART)*
                    param->table->actual_n_key_parts(keyinfo));
    }
  }
  DBUG_RETURN(quick);
}


void SEL_ARG::store_next_min_max_keys(KEY_PART *key,
                                      uchar **cur_min_key, uint *cur_min_flag,
                                      uchar **cur_max_key, uint *cur_max_flag,
                                      int *min_part, int *max_part)
{
  DBUG_ASSERT(next_key_part);
  const bool asc = !(key[next_key_part->part].flag & HA_REVERSE_SORT);

  if (!get_min_flag(key))
  {
    if (asc)
    {
      *min_part += next_key_part->store_min_key(key, cur_min_key,
                                                cur_min_flag, MAX_KEY, true);
    }
    else
    {
      uint tmp_flag = invert_min_flag(*cur_min_flag);
      *min_part += next_key_part->store_max_key(key, cur_min_key, &tmp_flag,
                                                MAX_KEY, true);
      *cur_min_flag = invert_max_flag(tmp_flag);
    }
  }
  if (!get_max_flag(key))
  {
    if (asc)
    {
      *max_part += next_key_part->store_max_key(key, cur_max_key,
                                                cur_max_flag, MAX_KEY, false);
    }
    else
    {
      uint tmp_flag = invert_max_flag(*cur_max_flag);
      *max_part += next_key_part->store_min_key(key, cur_max_key, &tmp_flag,
                                                MAX_KEY, false);
      *cur_max_flag = invert_min_flag(tmp_flag);
    }
  }
}

/*
** Fix this to get all possible sub_ranges
*/
bool
get_quick_keys(PARAM *param,QUICK_RANGE_SELECT *quick,KEY_PART *key,
	       SEL_ARG *key_tree, uchar *min_key,uint min_key_flag,
	       uchar *max_key, uint max_key_flag)
{
  QUICK_RANGE *range;
  uint flag;
  int min_part= key_tree->part-1, // # of keypart values in min_key buffer
      max_part= key_tree->part-1; // # of keypart values in max_key buffer

  const bool asc = !(key[key_tree->part].flag & HA_REVERSE_SORT);
  SEL_ARG *next_tree = asc ? key_tree->left : key_tree->right;
  if (next_tree != &null_element)
  {
    if (get_quick_keys(param,quick,key,next_tree,
		       min_key,min_key_flag, max_key, max_key_flag))
      return 1;
  }
  uchar *tmp_min_key=min_key,*tmp_max_key=max_key;

  key_tree->store_min_max(key, key[key_tree->part].store_length,
                          &tmp_min_key, min_key_flag,
                          &tmp_max_key, max_key_flag,
                          &min_part, &max_part);

  if (key_tree->next_key_part &&
      key_tree->next_key_part->type == SEL_ARG::KEY_RANGE &&
      key_tree->next_key_part->part == key_tree->part+1)
  {						  // const key as prefix
    if ((tmp_min_key - min_key) == (tmp_max_key - max_key) &&
         memcmp(min_key, max_key, (uint)(tmp_max_key - max_key))==0 &&
	 key_tree->min_flag==0 && key_tree->max_flag==0)
    {
      // psergey-note: simplified the parameters below as follows:
      //  min_key_flag | key_tree->min_flag   ->   min_key_flag
      //  max_key_flag | key_tree->max_flag   ->   max_key_flag
      if (get_quick_keys(param,quick,key,key_tree->next_key_part,
			 tmp_min_key, min_key_flag,
			 tmp_max_key, max_key_flag))
	return 1;
      goto end;					// Ugly, but efficient
    }
    {
      uint tmp_min_flag= key_tree->get_min_flag(key);
      uint tmp_max_flag= key_tree->get_max_flag(key);

      key_tree->store_next_min_max_keys(key,
                                        &tmp_min_key, &tmp_min_flag,
                                        &tmp_max_key, &tmp_max_flag,
                                        &min_part, &max_part);
      flag=tmp_min_flag | tmp_max_flag;
    }
  }
  else
  {
    if (asc)
    {
      flag= (key_tree->min_flag & GEOM_FLAG) ? key_tree->min_flag:
                                              (key_tree->min_flag |
                                              key_tree->max_flag);
    }
    else
    {
      // Invert flags for DESC keypart
      flag= invert_min_flag(key_tree->min_flag) |
            invert_max_flag(key_tree->max_flag);
    }
  }

  /*
    Ensure that some part of min_key and max_key are used.  If not,
    regard this as no lower/upper range
  */
  if ((flag & GEOM_FLAG) == 0)
  {
    if (tmp_min_key != param->min_key)
      flag&= ~NO_MIN_RANGE;
    else
      flag|= NO_MIN_RANGE;
    if (tmp_max_key != param->max_key)
      flag&= ~NO_MAX_RANGE;
    else
      flag|= NO_MAX_RANGE;
  }
  if (flag == 0)
  {
    uint length= (uint) (tmp_min_key - param->min_key);
    if (length == (uint) (tmp_max_key - param->max_key) &&
	!memcmp(param->min_key,param->max_key,length))
    {
      KEY *table_key=quick->head->key_info+quick->index;
      flag=EQ_RANGE;
      if ((table_key->flags & HA_NOSAME) &&
          min_part == key_tree->part &&
          key_tree->part == table_key->user_defined_key_parts-1)
      {
        DBUG_ASSERT(min_part == max_part);
        if ((table_key->flags & HA_NULL_PART_KEY) &&
            null_part_in_key(key,
                             param->min_key,
                             (uint) (tmp_min_key - param->min_key)))
          flag|= NULL_RANGE;
        else
          flag|= UNIQUE_RANGE;
      }
    }
  }

  /* Get range for retrieving rows in QUICK_SELECT::get_next */
  if (!(range= new (param->thd->mem_root) QUICK_RANGE(
                               param->thd,
                               param->min_key,
			       (uint) (tmp_min_key - param->min_key),
                               min_part >=0 ? make_keypart_map(min_part) : 0,
			       param->max_key,
			       (uint) (tmp_max_key - param->max_key),
                               max_part >=0 ? make_keypart_map(max_part) : 0,
			       flag)))
    return 1;			// out of memory

  set_if_bigger(quick->max_used_key_length, range->min_length);
  set_if_bigger(quick->max_used_key_length, range->max_length);
  set_if_bigger(quick->used_key_parts, (uint) key_tree->part+1);
  if (insert_dynamic(&quick->ranges, (uchar*) &range))
    return 1;

 end:
  next_tree= asc ? key_tree->right : key_tree->left;
  if (next_tree != &null_element)
    return get_quick_keys(param,quick,key,next_tree,
			  min_key,min_key_flag,
			  max_key,max_key_flag);
  return 0;
}

/*
  Return 1 if there is only one range and this uses the whole unique key
*/

bool QUICK_RANGE_SELECT::unique_key_range()
{
  if (ranges.elements == 1)
  {
    QUICK_RANGE *tmp= *((QUICK_RANGE**)ranges.buffer);
    if ((tmp->flag & (EQ_RANGE | NULL_RANGE)) == EQ_RANGE)
    {
      KEY *key=head->key_info+index;
      return (key->flags & HA_NOSAME) && key->key_length == tmp->min_length;
    }
  }
  return 0;
}



/*
  Return TRUE if any part of the key is NULL

  SYNOPSIS
    null_part_in_key()    
      key_part  Array of key parts (index description)
      key       Key values tuple
      length    Length of key values tuple in bytes.

  RETURN
    TRUE   The tuple has at least one "keypartX is NULL"
    FALSE  Otherwise
*/

static bool null_part_in_key(KEY_PART *key_part, const uchar *key, uint length)
{
  for (const uchar *end=key+length ;
       key < end;
       key+= key_part++->store_length)
  {
    if (key_part->null_bit && *key)
      return 1;
  }
  return 0;
}


bool QUICK_SELECT_I::is_keys_used(const MY_BITMAP *fields)
{
  return is_key_used(head, index, fields);
}

bool QUICK_INDEX_SORT_SELECT::is_keys_used(const MY_BITMAP *fields)
{
  QUICK_RANGE_SELECT *quick;
  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);
  while ((quick= it++))
  {
    if (is_key_used(head, quick->index, fields))
      return 1;
  }
  return 0;
}

bool QUICK_ROR_INTERSECT_SELECT::is_keys_used(const MY_BITMAP *fields)
{
  QUICK_SELECT_WITH_RECORD *qr;
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);
  while ((qr= it++))
  {
    if (is_key_used(head, qr->quick->index, fields))
      return 1;
  }
  return 0;
}

bool QUICK_ROR_UNION_SELECT::is_keys_used(const MY_BITMAP *fields)
{
  QUICK_SELECT_I *quick;
  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);
  while ((quick= it++))
  {
    if (quick->is_keys_used(fields))
      return 1;
  }
  return 0;
}


FT_SELECT *get_ft_select(THD *thd, TABLE *table, uint key)
{
  bool create_err= FALSE;
  FT_SELECT *fts= new FT_SELECT(thd, table, key, &create_err);
  if (create_err)
  {
    delete fts;
    return NULL;
  }
  else
    return fts;
}

/*
  Create quick select from ref/ref_or_null scan.

  SYNOPSIS
    get_quick_select_for_ref()
      thd      Thread handle
      table    Table to access
      ref      ref[_or_null] scan parameters
      records  Estimate of number of records (needed only to construct
               quick select)
  NOTES
    This allocates things in a new memory root, as this may be called many
    times during a query.

  RETURN
    Quick select that retrieves the same rows as passed ref scan
    NULL on error.
*/

QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
                                             TABLE_REF *ref, ha_rows records)
{
  MEM_ROOT *old_root, *alloc;
  QUICK_RANGE_SELECT *quick;
  KEY *key_info = &table->key_info[ref->key];
  KEY_PART *key_part;
  QUICK_RANGE *range;
  uint part;
  bool create_err= FALSE;
  Cost_estimate cost;
  uint max_used_key_len;

  old_root= thd->mem_root;
  /* The following call may change thd->mem_root */
  quick= new QUICK_RANGE_SELECT(thd, table, ref->key, 0, 0, &create_err);
  /* save mem_root set by QUICK_RANGE_SELECT constructor */
  alloc= thd->mem_root;
  /*
    return back default mem_root (thd->mem_root) changed by
    QUICK_RANGE_SELECT constructor
  */
  thd->mem_root= old_root;

  if (!quick || create_err || quick->init())
    goto err;
  quick->records= records;

  if ((cp_buffer_from_ref(thd, table, ref) &&
       unlikely(thd->is_fatal_error)) ||
      unlikely(!(range= new(alloc) QUICK_RANGE())))
    goto err;                                   // out of memory

  range->min_key= range->max_key= ref->key_buff;
  range->min_length= range->max_length= ref->key_length;
  range->min_keypart_map= range->max_keypart_map=
    make_prev_keypart_map(ref->key_parts);
  range->flag= EQ_RANGE;

  if (unlikely(!(quick->key_parts=key_part=(KEY_PART *)
                 alloc_root(&quick->alloc,sizeof(KEY_PART)*ref->key_parts))))
    goto err;
  
  max_used_key_len=0;
  for (part=0 ; part < ref->key_parts ;part++,key_part++)
  {
    key_part->part=part;
    key_part->field=        key_info->key_part[part].field;
    key_part->length=       key_info->key_part[part].length;
    key_part->store_length= key_info->key_part[part].store_length;
    key_part->null_bit=     key_info->key_part[part].null_bit;
    key_part->flag=         (uint8) key_info->key_part[part].key_part_flag;

    max_used_key_len +=key_info->key_part[part].store_length;
  }

  quick->max_used_key_length= max_used_key_len;

  if (insert_dynamic(&quick->ranges,(uchar*)&range))
    goto err;

  /*
     Add a NULL range if REF_OR_NULL optimization is used.
     For example:
       if we have "WHERE A=2 OR A IS NULL" we created the (A=2) range above
       and have ref->null_ref_key set. Will create a new NULL range here.
  */
  if (ref->null_ref_key)
  {
    QUICK_RANGE *null_range;

    *ref->null_ref_key= 1;		// Set null byte then create a range
    if (!(null_range= new (alloc)
          QUICK_RANGE(thd, ref->key_buff, ref->key_length,
                      make_prev_keypart_map(ref->key_parts),
                      ref->key_buff, ref->key_length,
                      make_prev_keypart_map(ref->key_parts), EQ_RANGE)))
      goto err;
    *ref->null_ref_key= 0;		// Clear null byte
    if (insert_dynamic(&quick->ranges,(uchar*)&null_range))
      goto err;
  }

  /* Call multi_range_read_info() to get the MRR flags and buffer size */
  quick->mrr_flags= HA_MRR_NO_ASSOCIATION | 
                    (table->file->keyread_enabled() ? HA_MRR_INDEX_ONLY : 0);
  if (thd->lex->sql_command != SQLCOM_SELECT)
    quick->mrr_flags |= HA_MRR_USE_DEFAULT_IMPL;

  quick->mrr_buf_size= thd->variables.mrr_buff_size;
  if (table->file->multi_range_read_info(quick->index, 1, (uint)records,
                                         ~0, 
                                         &quick->mrr_buf_size,
                                         &quick->mrr_flags, &cost))
    goto err;

  return quick;
err:
  delete quick;
  return 0;
}


/*
  Perform key scans for all used indexes (except CPK), get rowids and merge 
  them into an ordered non-recurrent sequence of rowids.
  
  The merge/duplicate removal is performed using Unique class. We put all
  rowids into Unique, get the sorted sequence and destroy the Unique.
  
  If table has a clustered primary key that covers all rows (TRUE for bdb
  and innodb currently) and one of the index_merge scans is a scan on PK,
  then rows that will be retrieved by PK scan are not put into Unique and 
  primary key scan is not performed here, it is performed later separately.

  RETURN
    0     OK
    other error
*/

int read_keys_and_merge_scans(THD *thd,
                              TABLE *head,
                              List<QUICK_RANGE_SELECT> quick_selects,
                              QUICK_RANGE_SELECT *pk_quick_select,
                              READ_RECORD *read_record,
                              bool intersection,
                              key_map *filtered_scans,
                              Unique **unique_ptr)
{
  List_iterator_fast<QUICK_RANGE_SELECT> cur_quick_it(quick_selects);
  QUICK_RANGE_SELECT* cur_quick;
  int result;
  Unique *unique= *unique_ptr;
  handler *file= head->file;
  bool with_cpk_filter= pk_quick_select != NULL;
  DBUG_ENTER("read_keys_and_merge");

  /* We're going to just read rowids. */
  head->prepare_for_position();

  cur_quick_it.rewind();
  cur_quick= cur_quick_it++;
  bool first_quick= TRUE;
  DBUG_ASSERT(cur_quick != 0);
  head->file->ha_start_keyread(cur_quick->index);
  
  /*
    We reuse the same instance of handler so we need to call both init and 
    reset here.
  */
  if (cur_quick->init() || cur_quick->reset())
    goto err;

  if (unique == NULL)
  {
    DBUG_EXECUTE_IF("index_merge_may_not_create_a_Unique", DBUG_SUICIDE(); );
    DBUG_EXECUTE_IF("only_one_Unique_may_be_created", 
                    DBUG_SET("+d,index_merge_may_not_create_a_Unique"); );

    unique= new Unique(refpos_order_cmp, (void *)file,
                       file->ref_length,
                       (size_t)thd->variables.sortbuff_size,
		       intersection ? quick_selects.elements : 0);                     
    if (!unique)
      goto err;
    *unique_ptr= unique;
  }
  else
  {
    unique->reset();
  }

  DBUG_ASSERT(file->ref_length == unique->get_size());
  DBUG_ASSERT(thd->variables.sortbuff_size == unique->get_max_in_memory_size());

  for (;;)
  {
    while ((result= cur_quick->get_next()) == HA_ERR_END_OF_FILE)
    {
      if (intersection)
        with_cpk_filter= filtered_scans->is_set(cur_quick->index);
      if (first_quick)
      {
        first_quick= FALSE;
        if (intersection && unique->is_in_memory())
          unique->close_for_expansion();
      }
      cur_quick->range_end();
      cur_quick= cur_quick_it++;
      if (!cur_quick)
        break;

      if (cur_quick->file->inited != handler::NONE) 
        cur_quick->file->ha_index_end();
      if (cur_quick->init() || cur_quick->reset())
        goto err;
    }

    if (result)
    {
      if (result != HA_ERR_END_OF_FILE)
      {
        cur_quick->range_end();
        goto err;
      }
      break;
    }

    if (thd->killed)
      goto err;

    if (with_cpk_filter &&
        pk_quick_select->row_in_ranges() != intersection )
      continue;

    cur_quick->file->position(cur_quick->record);
    if (unique->unique_add((char*)cur_quick->file->ref))
      goto err;
  }

  /*
    Ok all rowids are in the Unique now. The next call will initialize
    the unique structure so it can be used to iterate through the rowids
    sequence.
  */
  result= unique->get(head);
  /*
    index merge currently doesn't support "using index" at all
  */
  head->file->ha_end_keyread();
  if (init_read_record(read_record, thd, head, (SQL_SELECT*) 0,
                       &unique->sort, 1 , 1, TRUE))
    result= 1;
 DBUG_RETURN(result);

err:
  head->file->ha_end_keyread();
  DBUG_RETURN(1);
}


int QUICK_INDEX_MERGE_SELECT::read_keys_and_merge()

{
  int result;
  DBUG_ENTER("QUICK_INDEX_MERGE_SELECT::read_keys_and_merge");
  result= read_keys_and_merge_scans(thd, head, quick_selects, pk_quick_select,
                                    &read_record, FALSE, NULL, &unique);
  doing_pk_scan= FALSE;
  DBUG_RETURN(result);
}

/*
  Get next row for index_merge.
  NOTES
    The rows are read from
      1. rowids stored in Unique.
      2. QUICK_RANGE_SELECT with clustered primary key (if any).
    The sets of rows retrieved in 1) and 2) are guaranteed to be disjoint.
*/

int QUICK_INDEX_MERGE_SELECT::get_next()
{
  int result;
  DBUG_ENTER("QUICK_INDEX_MERGE_SELECT::get_next");

  if (doing_pk_scan)
    DBUG_RETURN(pk_quick_select->get_next());

  if ((result= read_record.read_record()) == -1)
  {
    result= HA_ERR_END_OF_FILE;
    end_read_record(&read_record);
    // Free things used by sort early. Shouldn't be strictly necessary
    unique->sort.reset();
    /* All rows from Unique have been retrieved, do a clustered PK scan */
    if (pk_quick_select)
    {
      doing_pk_scan= TRUE;
      if ((result= pk_quick_select->init()) ||
          (result= pk_quick_select->reset()))
        DBUG_RETURN(result);
      DBUG_RETURN(pk_quick_select->get_next());
    }
  }

  DBUG_RETURN(result);
}

int QUICK_INDEX_INTERSECT_SELECT::read_keys_and_merge()

{
  int result;
  DBUG_ENTER("QUICK_INDEX_INTERSECT_SELECT::read_keys_and_merge");
  result= read_keys_and_merge_scans(thd, head, quick_selects, pk_quick_select,
                                    &read_record, TRUE, &filtered_scans,
                                    &unique);
  DBUG_RETURN(result);
}

int QUICK_INDEX_INTERSECT_SELECT::get_next()
{
  int result;
  DBUG_ENTER("QUICK_INDEX_INTERSECT_SELECT::get_next");

  if ((result= read_record.read_record()) == -1)
  {
    result= HA_ERR_END_OF_FILE;
    end_read_record(&read_record);
    unique->sort.reset();                       // Free things early
  }

  DBUG_RETURN(result);
}


/*
  Retrieve next record.
  SYNOPSIS
     QUICK_ROR_INTERSECT_SELECT::get_next()

  NOTES
    Invariant on enter/exit: all intersected selects have retrieved all index
    records with rowid <= some_rowid_val and no intersected select has
    retrieved any index records with rowid > some_rowid_val.
    We start fresh and loop until we have retrieved the same rowid in each of
    the key scans or we got an error.

    If a Clustered PK scan is present, it is used only to check if row
    satisfies its condition (and never used for row retrieval).

    Locking: to ensure that exclusive locks are only set on records that
    are included in the final result we must release the lock
    on all rows we read but do not include in the final result. This
    must be done on each index that reads the record and the lock
    must be released using the same handler (the same quick object) as
    used when reading the record.

  RETURN
   0     - Ok
   other - Error code if any error occurred.
*/

int QUICK_ROR_INTERSECT_SELECT::get_next()
{
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> quick_it(quick_selects);
  QUICK_SELECT_WITH_RECORD *qr;
  QUICK_RANGE_SELECT* quick;

  /* quick that reads the given rowid first. This is needed in order
  to be able to unlock the row using the same handler object that locked
  it */
  QUICK_RANGE_SELECT* quick_with_last_rowid;

  int error, cmp;
  uint last_rowid_count=0;
  DBUG_ENTER("QUICK_ROR_INTERSECT_SELECT::get_next");

  /* Get a rowid for first quick and save it as a 'candidate' */
  qr= quick_it++;
  quick= qr->quick;
  error= quick->get_next();
  if (cpk_quick)
  {
    while (!error && !cpk_quick->row_in_ranges())
    {
      quick->file->unlock_row(); /* row not in range; unlock */
      error= quick->get_next();
    }
  }
  if (unlikely(error))
    DBUG_RETURN(error);

  /* Save the read key tuple */
  key_copy(qr->key_tuple, record, head->key_info + quick->index,
           quick->max_used_key_length);

  quick->file->position(quick->record);
  memcpy(last_rowid, quick->file->ref, head->file->ref_length);
  last_rowid_count= 1;
  quick_with_last_rowid= quick;

  while (last_rowid_count < quick_selects.elements)
  {
    if (!(qr= quick_it++))
    {
      quick_it.rewind();
      qr= quick_it++;
    }
    quick= qr->quick;

    do
    {
      DBUG_EXECUTE_IF("innodb_quick_report_deadlock",
                      DBUG_SET("+d,innodb_report_deadlock"););
      if (unlikely((error= quick->get_next())))
      {
        /* On certain errors like deadlock, trx might be rolled back.*/
        if (!thd->transaction_rollback_request)
          quick_with_last_rowid->file->unlock_row();
        DBUG_RETURN(error);
      }
      quick->file->position(quick->record);
      cmp= head->file->cmp_ref(quick->file->ref, last_rowid);
      if (cmp < 0)
      {
        /* This row is being skipped.  Release lock on it. */
        quick->file->unlock_row();
      }
    } while (cmp < 0);

    key_copy(qr->key_tuple, record, head->key_info + quick->index,
             quick->max_used_key_length);

    /* Ok, current select 'caught up' and returned ref >= cur_ref */
    if (cmp > 0)
    {
      /* Found a row with ref > cur_ref. Make it a new 'candidate' */
      if (cpk_quick)
      {
        while (!cpk_quick->row_in_ranges())
        {
          quick->file->unlock_row(); /* row not in range; unlock */
          if (unlikely((error= quick->get_next())))
          {
            /* On certain errors like deadlock, trx might be rolled back.*/
            if (!thd->transaction_rollback_request)
              quick_with_last_rowid->file->unlock_row();
            DBUG_RETURN(error);
          }
        }
        quick->file->position(quick->record);
      }
      memcpy(last_rowid, quick->file->ref, head->file->ref_length);
      quick_with_last_rowid->file->unlock_row();
      last_rowid_count= 1;
      quick_with_last_rowid= quick;

      //save the fields here
      key_copy(qr->key_tuple, record, head->key_info + quick->index,
               quick->max_used_key_length);
    }
    else
    {
      /* current 'candidate' row confirmed by this select */
      last_rowid_count++;
    }
  }

  /* We get here if we got the same row ref in all scans. */
  if (need_to_fetch_row)
    error= head->file->ha_rnd_pos(head->record[0], last_rowid);

  if (!need_to_fetch_row)
  {
    /* Restore the columns we've read/saved with other quick selects */
    quick_it.rewind();
    while ((qr= quick_it++))
    {
      if (qr->quick != quick)
      {
        key_restore(record, qr->key_tuple, head->key_info + qr->quick->index,
                    qr->quick->max_used_key_length);
      }
    }
  }

  DBUG_RETURN(error);
}


/*
  Retrieve next record.
  SYNOPSIS
    QUICK_ROR_UNION_SELECT::get_next()

  NOTES
    Enter/exit invariant:
    For each quick select in the queue a {key,rowid} tuple has been
    retrieved but the corresponding row hasn't been passed to output.

  RETURN
   0     - Ok
   other - Error code if any error occurred.
*/

int QUICK_ROR_UNION_SELECT::get_next()
{
  int error, dup_row;
  QUICK_SELECT_I *quick;
  uchar *tmp;
  DBUG_ENTER("QUICK_ROR_UNION_SELECT::get_next");

  do
  {
    if (!queue.elements)
      DBUG_RETURN(HA_ERR_END_OF_FILE);
    /* Ok, we have a queue with >= 1 scans */

    quick= (QUICK_SELECT_I*)queue_top(&queue);
    memcpy(cur_rowid, quick->last_rowid, rowid_length);

    /* put into queue rowid from the same stream as top element */
    if ((error= quick->get_next()))
    {
      if (error != HA_ERR_END_OF_FILE)
        DBUG_RETURN(error);
      queue_remove_top(&queue);
    }
    else
    {
      quick->save_last_pos();
      queue_replace_top(&queue);
    }

    if (!have_prev_rowid)
    {
      /* No rows have been returned yet */
      dup_row= FALSE;
      have_prev_rowid= TRUE;
    }
    else
      dup_row= !head->file->cmp_ref(cur_rowid, prev_rowid);
  } while (dup_row);

  tmp= cur_rowid;
  cur_rowid= prev_rowid;
  prev_rowid= tmp;

  error= head->file->ha_rnd_pos(quick->record, prev_rowid);
  DBUG_RETURN(error);
}


int QUICK_RANGE_SELECT::reset()
{
  uint  buf_size;
  uchar *mrange_buff;
  int   error;
  HANDLER_BUFFER empty_buf;
  MY_BITMAP * const save_read_set= head->read_set;
  MY_BITMAP * const save_write_set= head->write_set;
  DBUG_ENTER("QUICK_RANGE_SELECT::reset");
  last_range= NULL;
  cur_range= (QUICK_RANGE**) ranges.buffer;
  RANGE_SEQ_IF seq_funcs= {NULL, quick_range_seq_init, quick_range_seq_next, 0, 0};
  
  if (file->inited == handler::RND)
  {
    /* Handler could be left in this state by MRR */
    if (unlikely((error= file->ha_rnd_end())))
      DBUG_RETURN(error);
  }

  if (in_ror_merged_scan)
    head->column_bitmaps_set_no_signal(&column_bitmap, &column_bitmap);

  if (file->inited == handler::NONE)
  {
    DBUG_EXECUTE_IF("bug14365043_2",
                    DBUG_SET("+d,ha_index_init_fail"););
    if (unlikely((error= file->ha_index_init(index,1))))
    {
        file->print_error(error, MYF(0));
        goto err;
    }
  }

  /* Allocate buffer if we need one but haven't allocated it yet */
  if (mrr_buf_size && !mrr_buf_desc)
  {
    buf_size= mrr_buf_size;
    while (buf_size && !my_multi_malloc(key_memory_QUICK_RANGE_SELECT_mrr_buf_desc,
                                        MYF(MY_WME),
                                        &mrr_buf_desc, sizeof(*mrr_buf_desc),
                                        &mrange_buff, buf_size,
                                        NullS))
    {
      /* Try to shrink the buffers until both are 0. */
      buf_size/= 2;
    }
    if (!mrr_buf_desc)
    {
      error= HA_ERR_OUT_OF_MEM;
      goto err;
    }

    /* Initialize the handler buffer. */
    mrr_buf_desc->buffer= mrange_buff;
    mrr_buf_desc->buffer_end= mrange_buff + buf_size;
    mrr_buf_desc->end_of_used_area= mrange_buff;
  }

  if (!mrr_buf_desc)
    empty_buf.buffer= empty_buf.buffer_end= empty_buf.end_of_used_area= NULL;

  error= file->multi_range_read_init(&seq_funcs, (void*)this,
                                     (uint)ranges.elements, mrr_flags,
                                     mrr_buf_desc? mrr_buf_desc: &empty_buf);
err:
  /* Restore bitmaps set on entry */
  if (in_ror_merged_scan)
    head->column_bitmaps_set_no_signal(save_read_set, save_write_set);
  DBUG_RETURN(error);
}


/*
  Get next possible record using quick-struct.

  SYNOPSIS
    QUICK_RANGE_SELECT::get_next()

  NOTES
    Record is read into table->record[0]

  RETURN
    0			Found row
    HA_ERR_END_OF_FILE	No (more) rows in range
    #			Error code
*/

int QUICK_RANGE_SELECT::get_next()
{
  range_id_t dummy;
  int result;
  DBUG_ENTER("QUICK_RANGE_SELECT::get_next");

  if (!in_ror_merged_scan)
    DBUG_RETURN(file->multi_range_read_next(&dummy));

  MY_BITMAP * const save_read_set= head->read_set;
  MY_BITMAP * const save_write_set= head->write_set;
  /*
    We don't need to signal the bitmap change as the bitmap is always the
    same for this head->file
  */
  head->column_bitmaps_set_no_signal(&column_bitmap, &column_bitmap);
  result= file->multi_range_read_next(&dummy);
  head->column_bitmaps_set_no_signal(save_read_set, save_write_set);
  DBUG_RETURN(result);
}


/*
  Get the next record with a different prefix.

  @param prefix_length   length of cur_prefix
  @param group_key_parts The number of key parts in the group prefix
  @param cur_prefix      prefix of a key to be searched for

  Each subsequent call to the method retrieves the first record that has a
  prefix with length prefix_length and which is different from cur_prefix,
  such that the record with the new prefix is within the ranges described by
  this->ranges. The record found is stored into the buffer pointed by
  this->record. The method is useful for GROUP-BY queries with range
  conditions to discover the prefix of the next group that satisfies the range
  conditions.

  @todo

    This method is a modified copy of QUICK_RANGE_SELECT::get_next(), so both
    methods should be unified into a more general one to reduce code
    duplication.

  @retval 0                  on success
  @retval HA_ERR_END_OF_FILE if returned all keys
  @retval other              if some error occurred
*/

int QUICK_RANGE_SELECT::get_next_prefix(uint prefix_length,
                                        uint group_key_parts,
                                        uchar *cur_prefix)
{
  DBUG_ENTER("QUICK_RANGE_SELECT::get_next_prefix");
  const key_part_map keypart_map= make_prev_keypart_map(group_key_parts);

  for (;;)
  {
    int result;
    if (last_range)
    {
      /* Read the next record in the same range with prefix after cur_prefix. */
      DBUG_ASSERT(cur_prefix != NULL);
      result= file->ha_index_read_map(record, cur_prefix, keypart_map,
                                      HA_READ_AFTER_KEY);
      if (result || last_range->max_keypart_map == 0) {
        /*
          Only return if actual failure occurred. For HA_ERR_KEY_NOT_FOUND
          or HA_ERR_END_OF_FILE, we just want to continue to reach the next
          set of ranges. It is possible for the storage engine to return
          HA_ERR_KEY_NOT_FOUND/HA_ERR_END_OF_FILE even when there are more
          keys if it respects the end range set by the read_range_first call
          below.
        */
        if (result != HA_ERR_KEY_NOT_FOUND && result != HA_ERR_END_OF_FILE)
          DBUG_RETURN(result);
      } else {
        /*
          For storage engines that don't respect end range, check if we've
          moved past the current range.
        */
        key_range previous_endpoint;
        last_range->make_max_endpoint(&previous_endpoint, prefix_length,
                                      keypart_map);
        if (file->compare_key(&previous_endpoint) <= 0)
          DBUG_RETURN(0);
      }
    }

    size_t count= ranges.elements - (size_t)(cur_range - (QUICK_RANGE**) ranges.buffer);
    if (count == 0)
    {
      /* Ranges have already been used up before. None is left for read. */
      last_range= 0;
      DBUG_RETURN(HA_ERR_END_OF_FILE);
    }
    last_range= *(cur_range++);

    key_range start_key, end_key;
    last_range->make_min_endpoint(&start_key, prefix_length, keypart_map);
    last_range->make_max_endpoint(&end_key, prefix_length, keypart_map);

    result= file->read_range_first(last_range->min_keypart_map ? &start_key : 0,
				   last_range->max_keypart_map ? &end_key : 0,
                                   MY_TEST(last_range->flag & EQ_RANGE),
				   TRUE);
    if (last_range->flag == (UNIQUE_RANGE | EQ_RANGE))
      last_range= 0;			// Stop searching

    if (result != HA_ERR_END_OF_FILE)
      DBUG_RETURN(result);
    last_range= 0;			// No matching rows; go to next range
  }
}


/* Get next for geometrical indexes */

int QUICK_RANGE_SELECT_GEOM::get_next()
{
  DBUG_ENTER("QUICK_RANGE_SELECT_GEOM::get_next");

  for (;;)
  {
    int result;
    if (last_range)
    {
      // Already read through key
      result= file->ha_index_next_same(record, last_range->min_key,
                                       last_range->min_length);
      if (result != HA_ERR_END_OF_FILE)
	DBUG_RETURN(result);
    }

    size_t count= ranges.elements - (size_t)(cur_range - (QUICK_RANGE**) ranges.buffer);
    if (count == 0)
    {
      /* Ranges have already been used up before. None is left for read. */
      last_range= 0;
      DBUG_RETURN(HA_ERR_END_OF_FILE);
    }
    last_range= *(cur_range++);

    result= file->ha_index_read_map(record, last_range->min_key,
                                    last_range->min_keypart_map,
                                    (ha_rkey_function)(last_range->flag ^
                                                       GEOM_FLAG));
    if (result != HA_ERR_KEY_NOT_FOUND && result != HA_ERR_END_OF_FILE)
      DBUG_RETURN(result);
    last_range= 0;				// Not found, to next range
  }
}


/*
  Check if current row will be retrieved by this QUICK_RANGE_SELECT

  NOTES
    It is assumed that currently a scan is being done on another index
    which reads all necessary parts of the index that is scanned by this
    quick select.
    The implementation does a binary search on sorted array of disjoint
    ranges, without taking size of range into account.

    This function is used to filter out clustered PK scan rows in
    index_merge quick select.

  RETURN
    TRUE  if current row will be retrieved by this quick select
    FALSE if not
*/

bool QUICK_RANGE_SELECT::row_in_ranges()
{
  QUICK_RANGE *res;
  size_t min= 0;
  size_t max= ranges.elements - 1;
  size_t mid= (max + min)/2;

  while (min != max)
  {
    if (cmp_next(*(QUICK_RANGE**)dynamic_array_ptr(&ranges, mid)))
    {
      /* current row value > mid->max */
      min= mid + 1;
    }
    else
      max= mid;
    mid= (min + max) / 2;
  }
  res= *(QUICK_RANGE**)dynamic_array_ptr(&ranges, mid);
  return (!cmp_next(res) && !cmp_prev(res));
}

/*
  This is a hack: we inherit from QUICK_RANGE_SELECT so that we can use the
  get_next() interface, but we have to hold a pointer to the original
  QUICK_RANGE_SELECT because its data are used all over the place. What
  should be done is to factor out the data that is needed into a base
  class (QUICK_SELECT), and then have two subclasses (_ASC and _DESC)
  which handle the ranges and implement the get_next() function.  But
  for now, this seems to work right at least.
 */

QUICK_SELECT_DESC::QUICK_SELECT_DESC(QUICK_RANGE_SELECT *q,
                                     uint used_key_parts_arg)
 :QUICK_RANGE_SELECT(*q), rev_it(rev_ranges),
  used_key_parts (used_key_parts_arg)
{
  QUICK_RANGE *r;
  /*
    Use default MRR implementation for reverse scans. No table engine
    currently can do an MRR scan with output in reverse index order.
  */
  mrr_buf_desc= NULL;
  mrr_flags |= HA_MRR_USE_DEFAULT_IMPL;
  mrr_buf_size= 0;

  QUICK_RANGE **pr= (QUICK_RANGE**)ranges.buffer;
  QUICK_RANGE **end_range= pr + ranges.elements;
  for (; pr!=end_range; pr++)
    rev_ranges.push_front(*pr);

  /* Remove EQ_RANGE flag for keys that are not using the full key */
  for (r = rev_it++; r; r = rev_it++)
  {
    if ((r->flag & EQ_RANGE) &&
	head->key_info[index].key_length != r->max_length)
      r->flag&= ~EQ_RANGE;
  }
  rev_it.rewind();
  q->dont_free=1;				// Don't free shared mem
}

/**
  Helper function for QUICK_SELECT_DESC::get_next(), below, which sets the
  minimum endpoint as the end range on the storage engine when scanning in
  descending order.

  @param file        storage engine handler
  @param last_range  the range under inspection by QUICK_SELECT_DESC::get_next()
 */
static void set_min_range(handler *file, QUICK_RANGE *last_range)
{
  key_range min_range;
  last_range->make_min_endpoint(&min_range);
  if (min_range.length > 0)
    file->set_end_range(&min_range, handler::RANGE_SCAN_DESC);
  else
    file->set_end_range(nullptr);
}


int QUICK_SELECT_DESC::get_next()
{
  DBUG_ENTER("QUICK_SELECT_DESC::get_next");

  /* The max key is handled as follows:
   *   - if there is NO_MAX_RANGE, start at the end and move backwards
   *   - if it is an EQ_RANGE, which means that max key covers the entire
   *     key, go directly to the key and read through it (sorting backwards is
   *     same as sorting forwards)
   *   - if it is NEAR_MAX, go to the key or next, step back once, and
   *     move backwards
   *   - otherwise (not NEAR_MAX == include the key), go after the key,
   *     step back once, and move backwards
   */

  for (;; last_range= nullptr, file->set_end_range(nullptr))
  {
    int result;
    if (last_range)
    {						// Already read through key
      result = ((last_range->flag & EQ_RANGE && 
                 used_key_parts <= head->key_info[index].user_defined_key_parts) ? 
                file->ha_index_next_same(record, last_range->min_key,
                                      last_range->min_length) :
                file->ha_index_prev(record));
      if (!result)
      {
	if (cmp_prev(*rev_it.ref()) == 0)
	  DBUG_RETURN(0);
      }
      else if (result != HA_ERR_END_OF_FILE)
	DBUG_RETURN(result);
    }

    if (!(last_range= rev_it++))
      DBUG_RETURN(HA_ERR_END_OF_FILE);		// All ranges used

    key_range       start_key;
    start_key.key=    (const uchar*) last_range->min_key;
    start_key.length= last_range->min_length;
    start_key.flag=   ((last_range->flag & NEAR_MIN) ? HA_READ_AFTER_KEY :
                       (last_range->flag & EQ_RANGE) ?
                       HA_READ_KEY_EXACT : HA_READ_KEY_OR_NEXT);
    start_key.keypart_map= last_range->min_keypart_map;
    key_range       end_key;
    end_key.key=      (const uchar*) last_range->max_key;
    end_key.length=   last_range->max_length;
    end_key.flag=     (last_range->flag & NEAR_MAX ? HA_READ_BEFORE_KEY :
                       HA_READ_AFTER_KEY);
    end_key.keypart_map= last_range->max_keypart_map;
    result= file->prepare_range_scan((last_range->flag & NO_MIN_RANGE) ? NULL : &start_key,
                                     (last_range->flag & NO_MAX_RANGE) ? NULL : &end_key);
    if (result)
    {
      DBUG_RETURN(result);
    }

    if (last_range->flag & NO_MAX_RANGE)        // Read last record
    {
      set_min_range(file, last_range);
      int local_error;
      if (unlikely((local_error= file->ha_index_last(record))))
      {
        if (local_error != HA_ERR_KEY_NOT_FOUND &&
            local_error != HA_ERR_END_OF_FILE)
          DBUG_RETURN(local_error);

        // Nothing found in this range, go to next range
        continue;
      }
      if (cmp_prev(last_range) == 0)
        DBUG_RETURN(0);
      // No match; go to next range
      continue;
    }

    // Case where we can avoid descending scan, see comment above
    const bool eqrange_all_keyparts= (last_range->flag & EQ_RANGE) &&
                          (used_key_parts <= head->key_info[index].user_defined_key_parts);

    if (eqrange_all_keyparts)
    {
      file->set_end_range(NULL, handler::RANGE_SCAN_ASC);
      result= file->ha_index_read_map(record, last_range->max_key,
                                      last_range->max_keypart_map,
                                      HA_READ_KEY_EXACT);
    }
    else
    {
      set_min_range(file, last_range);
      DBUG_ASSERT(last_range->flag & NEAR_MAX ||
                  (last_range->flag & EQ_RANGE && 
                   used_key_parts > head->key_info[index].user_defined_key_parts) ||
                  range_reads_after_key(last_range));
      result= file->ha_index_read_map(record, last_range->max_key,
                                      last_range->max_keypart_map,
                                      ((last_range->flag & NEAR_MAX) ?
                                       HA_READ_BEFORE_KEY :
                                       HA_READ_PREFIX_LAST_OR_PREV));
    }
    if (result)
    {
      if (result != HA_ERR_KEY_NOT_FOUND && result != HA_ERR_END_OF_FILE)
	DBUG_RETURN(result);
      // Not found, to next range
      continue;
    }
    if (cmp_prev(last_range) == 0)
    {
      if (last_range->flag == (UNIQUE_RANGE | EQ_RANGE))
	last_range= 0;				// Stop searching
      DBUG_RETURN(0);				// Found key is in range
    }
    // To next range
  }
}


/**
  Create a compatible quick select with the result ordered in an opposite way

  @param used_key_parts_arg  Number of used key parts

  @retval NULL in case of errors (OOM etc)
  @retval pointer to a newly created QUICK_SELECT_DESC if success
*/

QUICK_SELECT_I *QUICK_RANGE_SELECT::make_reverse(uint used_key_parts_arg)
{
  QUICK_SELECT_DESC *new_quick= new QUICK_SELECT_DESC(this, used_key_parts_arg);
  if (new_quick == NULL)
  {
    delete new_quick;
    return NULL;
  }
  return new_quick;
}


/*
  Compare if found key is over max-value
  Returns 0 if key <= range->max_key
  TODO: Figure out why can't this function be as simple as cmp_prev(). 
*/

int QUICK_RANGE_SELECT::cmp_next(QUICK_RANGE *range_arg)
{
  if (range_arg->flag & NO_MAX_RANGE)
    return 0;                                   /* key can't be to large */

  KEY_PART *key_part=key_parts;
  uint store_length;

  for (uchar *key=range_arg->max_key, *end=key+range_arg->max_length;
       key < end;
       key+= store_length, key_part++)
  {
    int cmp;
    bool reverse= MY_TEST(key_part->flag & HA_REVERSE_SORT);
    store_length= key_part->store_length;
    if (key_part->null_bit)
    {
      if (*key)
      {
        if (!key_part->field->is_null())
          return reverse ? 0 : 1;
        continue;
      }
      else if (key_part->field->is_null())
        return reverse ? 1 : 0;
      key++;					// Skip null byte
      store_length--;
    }
    if ((cmp=key_part->field->key_cmp(key, key_part->length)) < 0)
      return reverse ? 1 : 0;
    if (cmp > 0)
      return reverse ? 0 : 1;
  }
  return (range_arg->flag & NEAR_MAX) ? 1 : 0;          // Exact match
}


/*
  Returns 0 if found key is inside range (found key >= range->min_key).
*/

int QUICK_RANGE_SELECT::cmp_prev(QUICK_RANGE *range_arg)
{
  int cmp;
  if (range_arg->flag & NO_MIN_RANGE)
    return 0;					/* key can't be to small */

  cmp= key_cmp(key_part_info, range_arg->min_key,
               range_arg->min_length);
  if (cmp > 0 || (cmp == 0 && !(range_arg->flag & NEAR_MIN)))
    return 0;
  return 1;                                     // outside of range
}


/*
 * TRUE if this range will require using HA_READ_AFTER_KEY
   See comment in get_next() about this
 */

bool QUICK_SELECT_DESC::range_reads_after_key(QUICK_RANGE *range_arg)
{
  return ((range_arg->flag & (NO_MAX_RANGE | NEAR_MAX)) ||
	  !(range_arg->flag & EQ_RANGE) ||
	  head->key_info[index].key_length != range_arg->max_length) ? 1 : 0;
}


void QUICK_SELECT_I::add_key_name(String *str, bool *first)
{
  KEY *key_info= head->key_info + index;

  if (*first)
    *first= FALSE;
  else
    str->append(',');
  str->append(&key_info->name);
}
 

Explain_quick_select* QUICK_RANGE_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  if ((res= new (local_alloc) Explain_quick_select(QS_TYPE_RANGE)))
    res->range.set(local_alloc, &head->key_info[index], max_used_key_length);
  return res;
}


Explain_quick_select*
QUICK_GROUP_MIN_MAX_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  if ((res= new (local_alloc) Explain_quick_select(QS_TYPE_GROUP_MIN_MAX)))
    res->range.set(local_alloc, &head->key_info[index], max_used_key_length);
  return res;
}


Explain_quick_select*
QUICK_INDEX_SORT_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  if (!(res= new (local_alloc) Explain_quick_select(get_type())))
    return NULL;

  QUICK_RANGE_SELECT *quick;
  Explain_quick_select *child_explain;
  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);
  while ((quick= it++))
  {
    if ((child_explain= quick->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }

  if (pk_quick_select)
  {
    if ((child_explain= pk_quick_select->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }
  return res;
}


/*
  Same as QUICK_INDEX_SORT_SELECT::get_explain(), but primary key is printed
  first
*/

Explain_quick_select*
QUICK_INDEX_INTERSECT_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  Explain_quick_select *child_explain;

  if (!(res= new (local_alloc) Explain_quick_select(get_type())))
    return NULL;

  if (pk_quick_select)
  {
    if ((child_explain= pk_quick_select->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }

  QUICK_RANGE_SELECT *quick;
  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);
  while ((quick= it++))
  {
    if ((child_explain= quick->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }
  return res;
}


Explain_quick_select*
QUICK_ROR_INTERSECT_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  Explain_quick_select *child_explain;

  if (!(res= new (local_alloc) Explain_quick_select(get_type())))
    return NULL;

  QUICK_SELECT_WITH_RECORD *qr;
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);
  while ((qr= it++))
  {
    if ((child_explain= qr->quick->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }

  if (cpk_quick)
  {
    if ((child_explain= cpk_quick->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }
  return res;
}


Explain_quick_select*
QUICK_ROR_UNION_SELECT::get_explain(MEM_ROOT *local_alloc)
{
  Explain_quick_select *res;
  Explain_quick_select *child_explain;

  if (!(res= new (local_alloc) Explain_quick_select(get_type())))
    return NULL;

  QUICK_SELECT_I *quick;
  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);
  while ((quick= it++))
  {
    if ((child_explain= quick->get_explain(local_alloc)))
      res->children.push_back(child_explain);
    else
      return NULL;
  }

  return res;
}


void QUICK_SELECT_I::add_key_and_length(String *key_names,
                                        String *used_lengths,
                                        bool *first)
{
  char buf[64];
  size_t length;
  KEY *key_info= head->key_info + index;

  if (*first)
    *first= FALSE;
  else
  {
    key_names->append(',');
    used_lengths->append(',');
  }
  key_names->append(&key_info->name);
  length= longlong10_to_str(max_used_key_length, buf, 10) - buf;
  used_lengths->append(buf, length);
}


void QUICK_RANGE_SELECT::add_keys_and_lengths(String *key_names,
                                              String *used_lengths)
{
  bool first= TRUE;

  add_key_and_length(key_names, used_lengths, &first);
}

void QUICK_INDEX_MERGE_SELECT::add_keys_and_lengths(String *key_names,
                                                    String *used_lengths)
{
  QUICK_RANGE_SELECT *quick;
  bool first= TRUE;

  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);

  while ((quick= it++))
  {
    quick->add_key_and_length(key_names, used_lengths, &first);
  }

  if (pk_quick_select)
    pk_quick_select->add_key_and_length(key_names, used_lengths, &first);
}


void QUICK_INDEX_INTERSECT_SELECT::add_keys_and_lengths(String *key_names,
                                                        String *used_lengths)
{
  QUICK_RANGE_SELECT *quick;
  bool first= TRUE;

  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);

  if (pk_quick_select)
    pk_quick_select->add_key_and_length(key_names, used_lengths, &first);

  while ((quick= it++))
  {
    quick->add_key_and_length(key_names, used_lengths, &first);
  }
}

void QUICK_ROR_INTERSECT_SELECT::add_keys_and_lengths(String *key_names,
                                                      String *used_lengths)
{
  QUICK_SELECT_WITH_RECORD *qr;
  bool first= TRUE;

  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);

  while ((qr= it++))
  {
    qr->quick->add_key_and_length(key_names, used_lengths, &first);
  }
  if (cpk_quick)
    cpk_quick->add_key_and_length(key_names, used_lengths, &first);
}

void QUICK_ROR_UNION_SELECT::add_keys_and_lengths(String *key_names,
                                                  String *used_lengths)
{
  QUICK_SELECT_I *quick;
  bool first= TRUE;

  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);

  while ((quick= it++))
  {
    if (first)
      first= FALSE;
    else
    {
      used_lengths->append(',');
      key_names->append(',');
    }
    quick->add_keys_and_lengths(key_names, used_lengths);
  }
}


void QUICK_RANGE_SELECT::add_used_key_part_to_set()
{
  uint key_len;
  KEY_PART *part= key_parts;
  for (key_len=0; key_len < max_used_key_length;
       key_len += (part++)->store_length)
  {
    /*
      We have to use field_index instead of part->field
      as for partial fields, part->field points to
      a temporary field that is only part of the original
      field.  field_index always points to the original field
    */
    Field *field= head->field[part->field->field_index];
    field->register_field_in_read_map();
  }
}


void QUICK_GROUP_MIN_MAX_SELECT::add_used_key_part_to_set()
{
  uint key_len;
  KEY_PART_INFO *part= index_info->key_part;
  for (key_len=0; key_len < max_used_key_length;
       key_len += (part++)->store_length)
  {
    /*
      We have to use field_index instead of part->field
      as for partial fields, part->field points to
      a temporary field that is only part of the original
      field.  field_index always points to the original field
    */
    Field *field= head->field[part->field->field_index];
    field->register_field_in_read_map();
  }
}


void QUICK_ROR_INTERSECT_SELECT::add_used_key_part_to_set()
{
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);
  QUICK_SELECT_WITH_RECORD *quick;
  while ((quick= it++))
  {
    quick->quick->add_used_key_part_to_set();
  }
}


void QUICK_INDEX_SORT_SELECT::add_used_key_part_to_set()
{
  QUICK_RANGE_SELECT *quick;
  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);
  while ((quick= it++))
  {
    quick->add_used_key_part_to_set();
  }
  if (pk_quick_select)
    pk_quick_select->add_used_key_part_to_set();
}


void QUICK_ROR_UNION_SELECT::add_used_key_part_to_set()
{
  QUICK_SELECT_I *quick;
  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);

  while ((quick= it++))
  {
    quick->add_used_key_part_to_set();
  }
}


/*******************************************************************************
* Implementation of QUICK_GROUP_MIN_MAX_SELECT
*******************************************************************************/

static inline uint get_field_keypart(KEY *index, Field *field);
static bool get_sel_arg_for_keypart(Field *field, SEL_ARG *index_range_tree,
                                    SEL_ARG **cur_range);
static bool get_constant_key_infix(KEY *index_info, SEL_ARG *index_range_tree,
                       KEY_PART_INFO *first_non_group_part,
                       KEY_PART_INFO *min_max_arg_part,
                       KEY_PART_INFO *last_part, THD *thd,
                       uchar *key_infix, uint *key_infix_len,
                       KEY_PART_INFO **first_non_infix_part);
static bool
check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
                               Field::imagetype image_type,
                               bool *has_min_max_fld, bool *has_other_fld);

static void
cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
                   uint group_key_parts, SEL_TREE *range_tree,
                   SEL_ARG *index_tree, ha_rows quick_prefix_records,
                   bool have_min, bool have_max,
                   double *read_cost, ha_rows *records);


/*
  @brief
    Check if index keynr is clustered and the query only uses its explicitly
    defined parts.

  @detail
    Clustered PK indexes are not present in table->covering_keys (one can say
    a clustered index is always covering as it has all table's fields in it).
    This function checks if the set of columns in the index definition
    PRIMARY KEY(col1, ... colN) is covering for the quey.
*/

static bool index_is_clustered_covering(const TABLE *table, uint keynr)
{
  if (!table->file->is_clustering_key(keynr))
    return false;

  /*
    Check that all fields used by the query are explicitly present
    in the index.
  */
  for (uint i= bitmap_get_first_set(table->read_set);
       i != MY_BIT_NONE;
       i= bitmap_get_next_set(table->read_set, i))
  {
    if (!table->field[i]->part_of_key.is_set(keynr))
      return false;
  }
  return true;
}


/**
  Test if this access method is applicable to a GROUP query with MIN/MAX
  functions, and if so, construct a new TRP object.

  DESCRIPTION
    Test whether a query can be computed via a QUICK_GROUP_MIN_MAX_SELECT.
    Queries computable via a QUICK_GROUP_MIN_MAX_SELECT must satisfy the
    following conditions:
    A) Table T has at least one compound index I of the form:
       I = <A_1, ...,A_k, [B_1,..., B_m], C, [D_1,...,D_n]>
    B) Query conditions:
    B0. Q is over a single table T.
    B1. The attributes referenced by Q are a subset of the attributes of I.
    B2. All attributes QA in Q can be divided into 3 overlapping groups:
        - SA = {S_1, ..., S_l, [C]} - from the SELECT clause, where C is
          referenced by any number of MIN and/or MAX functions if present.
        - WA = {W_1, ..., W_p} - from the WHERE clause
        - GA = <G_1, ..., G_k> - from the GROUP BY clause (if any)
             = SA              - if Q is a DISTINCT query (based on the
                                 equivalence of DISTINCT and GROUP queries.
        - NGA = QA - (GA union C) = {NG_1, ..., NG_m} - the ones not in
          GROUP BY and not referenced by MIN/MAX functions.
        with the following properties specified below.
    B3. If Q has a GROUP BY WITH ROLLUP clause the access method is not 
        applicable.

    SA1. There is at most one attribute in SA referenced by any number of
         MIN and/or MAX functions which, which if present, is denoted as C.
    SA2. The position of the C attribute in the index is after the last A_k.
    SA3. The attribute C can be referenced in the WHERE clause only in
         predicates of the forms:
         - (C {< | <= | > | >= | =} const)
         - (const {< | <= | > | >= | =} C)
         - (C between const_i and const_j)
         - C IS NULL
         - C IS NOT NULL
         - C != const  (unless C is the primary key)
    SA4. If Q has a GROUP BY clause, there are no other aggregate functions
         except MIN and MAX. For queries with DISTINCT, aggregate functions
         are allowed.
    SA5. The select list in DISTINCT queries should not contain expressions.
    SA6. Clustered index can not be used by GROUP_MIN_MAX quick select
         for AGG_FUNC(DISTINCT ...) optimization because cursor position is
         never stored after a unique key lookup in the clustered index and
         furhter index_next/prev calls can not be used. So loose index scan
         optimization can not be used in this case.
    SA7. If Q has both AGG_FUNC(DISTINCT ...) and MIN/MAX() functions then this
         access method is not used.
         For above queries MIN/MAX() aggregation has to be done at
         nested_loops_join (end_send_group). But with current design MIN/MAX()
         is always set as part of loose index scan. Because of this mismatch
         MIN() and MAX() values will be set incorrectly. For such queries to
         work we need a new interface for loose index scan. This new interface
         should only fetch records with min and max values and let
         end_send_group to do aggregation. Until then do not use
         loose_index_scan.
    GA1. If Q has a GROUP BY clause, then GA is a prefix of I. That is, if
         G_i = A_j => i = j.
    GA2. If Q has a DISTINCT clause, then there is a permutation of SA that
         forms a prefix of I. This permutation is used as the GROUP clause
         when the DISTINCT query is converted to a GROUP query.
    GA3. The attributes in GA may participate in arbitrary predicates, divided
         into two groups:
         - RNG(G_1,...,G_q ; where q <= k) is a range condition over the
           attributes of a prefix of GA
         - PA(G_i1,...G_iq) is an arbitrary predicate over an arbitrary subset
           of GA. Since P is applied to only GROUP attributes it filters some
           groups, and thus can be applied after the grouping.
    GA4. There are no expressions among G_i, just direct column references.
    NGA1.If in the index I there is a gap between the last GROUP attribute G_k,
         and the MIN/MAX attribute C, then NGA must consist of exactly the
         index attributes that constitute the gap. As a result there is a
         permutation of NGA, BA=<B_1,...,B_m>, that coincides with the gap
         in the index.
    NGA2.If BA <> {}, then the WHERE clause must contain a conjunction EQ of
         equality conditions for all NG_i of the form (NG_i = const) or
         (const = NG_i), such that each NG_i is referenced in exactly one
         conjunct. Informally, the predicates provide constants to fill the
         gap in the index.
    NGA3.If BA <> {}, there can only be one range. TODO: This is a code
         limitation and is not strictly needed. See BUG#15947433
    WA1. There are no other attributes in the WHERE clause except the ones
         referenced in predicates RNG, PA, PC, EQ defined above. Therefore
         WA is subset of (GA union NGA union C) for GA,NGA,C that pass the
         above tests. By transitivity then it also follows that each WA_i
         participates in the index I (if this was already tested for GA, NGA
         and C).
    WA2. If there is a predicate on C, then it must be in conjunction
         to all predicates on all earlier keyparts in I.

    C) Overall query form:
       SELECT EXPR([A_1,...,A_k], [B_1,...,B_m], [MIN(C)], [MAX(C)])
         FROM T
        WHERE [RNG(A_1,...,A_p ; where p <= k)]
         [AND EQ(B_1,...,B_m)]
         [AND PC(C)]
         [AND PA(A_i1,...,A_iq)]
       GROUP BY A_1,...,A_k
       [HAVING PH(A_1, ..., B_1,..., C)]
    where EXPR(...) is an arbitrary expression over some or all SELECT fields,
    or:
       SELECT DISTINCT A_i1,...,A_ik
         FROM T
        WHERE [RNG(A_1,...,A_p ; where p <= k)]
         [AND PA(A_i1,...,A_iq)];

  NOTES
    If the current query satisfies the conditions above, and if
    (mem_root! = NULL), then the function constructs and returns a new TRP
    object, that is later used to construct a new QUICK_GROUP_MIN_MAX_SELECT.
    If (mem_root == NULL), then the function only tests whether the current
    query satisfies the conditions above, and, if so, sets
    is_applicable = TRUE.

    Queries with DISTINCT for which index access can be used are transformed
    into equivalent group-by queries of the form:

    SELECT A_1,...,A_k FROM T
     WHERE [RNG(A_1,...,A_p ; where p <= k)]
      [AND PA(A_i1,...,A_iq)]
    GROUP BY A_1,...,A_k;

    The group-by list is a permutation of the select attributes, according
    to their order in the index.

  EXAMPLES of handled queries
    select max(keypart2) from t1 group by keypart1
    select max(keypart2) from t1 where  keypart2 <= const group by keypart1
    select distinct keypart1 from table;
    select count(distinct keypart1) from table;

  TODO
  - What happens if the query groups by the MIN/MAX field, and there is no
    other field as in: "select MY_MIN(a) from t1 group by a" ?
  - We assume that the general correctness of the GROUP-BY query was checked
    before this point. Is this correct, or do we have to check it completely?
  - Lift the limitation in condition (B3), that is, make this access method 
    applicable to ROLLUP queries.

 @param  param     Parameter from test_quick_select
 @param  sel_tree  Range tree generated by get_mm_tree
 @param  read_time Best read time so far of table or index scan time
 @return table read plan
   @retval NULL  Loose index scan not applicable or mem_root == NULL
   @retval !NULL Loose index scan table read plan
*/

static TRP_GROUP_MIN_MAX *
get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
{
  THD *thd= param->thd;
  JOIN *join= thd->lex->current_select->join;
  TABLE *table= param->table;
  bool have_min= FALSE;              /* TRUE if there is a MIN function. */
  bool have_max= FALSE;              /* TRUE if there is a MAX function. */
  Item_field *min_max_arg_item= NULL; // The argument of all MIN/MAX functions
  KEY_PART_INFO *min_max_arg_part= NULL; /* The corresponding keypart. */
  uint group_prefix_len= 0; /* Length (in bytes) of the key prefix. */
  KEY *index_info= NULL;    /* The index chosen for data access. */
  uint index= 0;            /* The id of the chosen index. */
  uint group_key_parts= 0;  // Number of index key parts in the group prefix.
  uint used_key_parts= 0;   /* Number of index key parts used for access. */
  uchar key_infix[MAX_KEY_LENGTH]; /* Constants from equality predicates.*/
  uint key_infix_len= 0;          /* Length of key_infix. */
  TRP_GROUP_MIN_MAX *read_plan= NULL; /* The eventually constructed TRP. */
  uint key_part_nr;
  uint elements_in_group;
  ORDER *tmp_group;
  Item *item;
  Item_field *item_field;
  bool is_agg_distinct;
  List<Item_field> agg_distinct_flds;
  DBUG_ENTER("get_best_group_min_max");

  Json_writer_object trace_group(thd, "group_index_range");
  const char* cause= NULL;

  /* Perform few 'cheap' tests whether this access method is applicable. */
  if (!join) /* This is not a select statement. */
    cause= "no join";
  else if (join->table_count != 1)  /* The query must reference one table. */
    cause= "not single_table";
  else if (join->select_lex->olap == ROLLUP_TYPE) /* Check (B3) for ROLLUP */
    cause= "rollup";
  else if (table->s->keys == 0)  // There are no indexes to use.
    cause= "no index";
  else if (join->conds && join->conds->used_tables()
          & OUTER_REF_TABLE_BIT) // Cannot execute with correlated conditions.
    cause= "correlated conditions";
  else if (table->stat_records() == 0)
    cause= "Empty table"; // Exit now, records=0 messes up cost computations

  if (cause)
  {
    trace_group.add("chosen", false).add("cause", cause);
    DBUG_RETURN(NULL);
  }

  is_agg_distinct = is_indexed_agg_distinct(join, &agg_distinct_flds);

  if ((!join->group_list) && /* Neither GROUP BY nor a DISTINCT query. */
      (!join->select_distinct) &&
      !is_agg_distinct)
  {
    if (unlikely(trace_group.trace_started()))
      trace_group.add("chosen", false).add("cause","no group by or distinct");
    DBUG_RETURN(NULL);
  }
  /* Analyze the query in more detail. */

  /* Check (SA1,SA4) and store the only MIN/MAX argument - the C attribute.*/
  List_iterator<Item> select_items_it(join->fields_list);

  if (join->sum_funcs[0])
  {
    Item_sum *min_max_item;
    Item_sum **func_ptr= join->sum_funcs;
    while ((min_max_item= *(func_ptr++)))
    {
      if (min_max_item->sum_func() == Item_sum::MIN_FUNC)
        have_min= TRUE;
      else if (min_max_item->sum_func() == Item_sum::MAX_FUNC)
        have_max= TRUE;
      else if (is_agg_distinct &&
               (min_max_item->sum_func() == Item_sum::COUNT_DISTINCT_FUNC ||
                min_max_item->sum_func() == Item_sum::SUM_DISTINCT_FUNC ||
                min_max_item->sum_func() == Item_sum::AVG_DISTINCT_FUNC))
        continue;
      else
      {
        if (unlikely(trace_group.trace_started()))
          trace_group.
            add("chosen", false).
            add("cause", "not applicable aggregate function");
        DBUG_RETURN(NULL);
      }

      /* The argument of MIN/MAX. */
      Item *expr= min_max_item->get_arg(0)->real_item();
      if (expr->type() == Item::FIELD_ITEM) /* Is it an attribute? */
      {
        if (! min_max_arg_item)
          min_max_arg_item= (Item_field*) expr;
        else if (! min_max_arg_item->eq(expr, 1))
        {
          if (unlikely(trace_group.trace_started()))
            trace_group.
              add("chosen", false).
              add("cause", "arguments different in min max function");
          DBUG_RETURN(NULL);
        }
      }
      else
      {
        if (unlikely(trace_group.trace_started()))
          trace_group.
            add("chosen", false).
            add("cause", "no field item in min max function");
        DBUG_RETURN(NULL);
      }
    }
  }

  /* Check (SA7). */
  if (is_agg_distinct && (have_max || have_min))
  {
    if (unlikely(trace_group.trace_started()))
      trace_group.
        add("chosen", false).
        add("cause", "have both agg distinct and min max");
    DBUG_RETURN(NULL);
  }

  /* Check (SA5). */
  if (join->select_distinct)
  {
    trace_group.add("distinct_query", true);
    while ((item= select_items_it++))
    {
      if (item->real_item()->type() != Item::FIELD_ITEM)
      {
        if (unlikely(trace_group.trace_started()))
          trace_group.
            add("chosen", false).
            add("cause", "distinct field is expression");
        DBUG_RETURN(NULL);
      }
    }
  }

  /* Check (GA4) - that there are no expressions among the group attributes. */
  elements_in_group= 0;
  for (tmp_group= join->group_list; tmp_group; tmp_group= tmp_group->next)
  {
    if ((*tmp_group->item)->real_item()->type() != Item::FIELD_ITEM)
    {
      if (unlikely(trace_group.trace_started()))
      trace_group.
        add("chosen", false).
        add("cause", "group field is expression");
      DBUG_RETURN(NULL);
    }
    elements_in_group++;
  }

  /*
    Check that table has at least one compound index such that the conditions
    (GA1,GA2) are all TRUE. If there is more than one such index, select the
    first one. Here we set the variables: group_prefix_len and index_info.
  */
  /* Cost-related variables for the best index so far. */
  double best_read_cost= DBL_MAX;
  ha_rows best_records= 0;
  SEL_ARG *best_index_tree= NULL;
  ha_rows best_quick_prefix_records= 0;
  uint best_param_idx= 0;

  const uint pk= param->table->s->primary_key;
  uint max_key_part;  
  SEL_ARG *cur_index_tree= NULL;
  ha_rows cur_quick_prefix_records= 0;

  // We go through allowed indexes
  Json_writer_array trace_indexes(thd, "potential_group_range_indexes");

  for (uint cur_param_idx= 0; cur_param_idx < param->keys ; ++cur_param_idx)
  {
    const uint cur_index= param->real_keynr[cur_param_idx];
    KEY *const cur_index_info= &table->key_info[cur_index];

    Json_writer_object trace_idx(thd);
    trace_idx.add("index", cur_index_info->name);

    KEY_PART_INFO *cur_part;
    KEY_PART_INFO *end_part; /* Last part for loops. */
    /* Last index part. */
    KEY_PART_INFO *last_part;
    KEY_PART_INFO *first_non_group_part;
    KEY_PART_INFO *first_non_infix_part;
    uint key_parts;
    uint key_infix_parts;
    uint cur_group_key_parts= 0;
    uint cur_group_prefix_len= 0;
    double cur_read_cost;
    ha_rows cur_records;
    key_map used_key_parts_map;
    uint cur_key_infix_len= 0;
    uchar cur_key_infix[MAX_KEY_LENGTH];
    uint cur_used_key_parts;
    
    /*
      Check (B1) - if current index is covering.
      (was also: "Exclude UNIQUE indexes ..." but this was removed because 
      there are cases Loose Scan over a multi-part index is useful).
    */
    if ((!table->covering_keys.is_set(cur_index) &&
         !index_is_clustered_covering(table, cur_index)) ||
        !table->keys_in_use_for_group_by.is_set(cur_index))
    {
      cause= "not covering";
      goto next_index;
    }

    /*
      This function is called on the precondition that the index is covering.
      Therefore if the GROUP BY list contains more elements than the index,
      these are duplicates. The GROUP BY list cannot be a prefix of the index.
    */
    if (elements_in_group > table->actual_n_key_parts(cur_index_info))
    {
      cause= "group key parts greater than index key parts";
      goto next_index;
    }
    
    /*
      Unless extended keys can be used for cur_index:
      If the current storage manager is such that it appends the primary key to
      each index, then the above condition is insufficient to check if the
      index is covering. In such cases it may happen that some fields are
      covered by the PK index, but not by the current index. Since we can't
      use the concatenation of both indexes for index lookup, such an index
      does not qualify as covering in our case. If this is the case, below
      we check that all query fields are indeed covered by 'cur_index'.
    */
    if (cur_index_info->user_defined_key_parts ==
        table->actual_n_key_parts(cur_index_info)
        && pk < MAX_KEY && cur_index != pk &&
        (table->file->ha_table_flags() & HA_PRIMARY_KEY_IN_READ_INDEX))
    {
      /* For each table field */
      for (uint i= 0; i < table->s->fields; i++)
      {
        Field *cur_field= table->field[i];
        /*
          If the field is used in the current query ensure that it's
          part of 'cur_index'
        */
        if (bitmap_is_set(table->read_set, cur_field->field_index) &&
            !cur_field->part_of_key_not_clustered.is_set(cur_index))
        {
          cause= "not covering";
          goto next_index;                  // Field was not part of key
        }
      }
    }

    trace_idx.add("covering", true);

    max_key_part= 0;
    used_key_parts_map.clear_all();

    /*
      Check (GA1) for GROUP BY queries.
    */
    if (join->group_list)
    {
      cur_part= cur_index_info->key_part;
      end_part= cur_part + table->actual_n_key_parts(cur_index_info);
      /* Iterate in parallel over the GROUP list and the index parts. */
      for (tmp_group= join->group_list; tmp_group && (cur_part != end_part);
           tmp_group= tmp_group->next, cur_part++)
      {
        /*
          TODO:
          tmp_group::item is an array of Item, is it OK to consider only the
          first Item? If so, then why? What is the array for?
        */
        /* Above we already checked that all group items are fields. */
        DBUG_ASSERT((*tmp_group->item)->real_item()->type() ==
                    Item::FIELD_ITEM);
        Item_field *group_field= (Item_field *) (*tmp_group->item)->real_item();
        if (group_field->field->eq(cur_part->field))
        {
          cur_group_prefix_len+= cur_part->store_length;
          ++cur_group_key_parts;
          max_key_part= (uint)(cur_part - cur_index_info->key_part) + 1;
          used_key_parts_map.set_bit(max_key_part);
        }
        else
        {
          cause= "group attribute not prefix in index";
          goto next_index;
        }
      }
    }
    /*
      Check (GA2) if this is a DISTINCT query.
      If GA2, then Store a new ORDER object in group_fields_array at the
      position of the key part of item_field->field. Thus we get the ORDER
      objects for each field ordered as the corresponding key parts.
      Later group_fields_array of ORDER objects is used to convert the query
      to a GROUP query.
    */
    if ((!join->group && join->select_distinct) ||
        is_agg_distinct)
    {
      if (!is_agg_distinct)
      {
        select_items_it.rewind();
      }

      List_iterator<Item_field> agg_distinct_flds_it (agg_distinct_flds);
      while (NULL != (item = (is_agg_distinct ?
             (Item *) agg_distinct_flds_it++ : select_items_it++)))
      {
        /* (SA5) already checked above. */
        item_field= (Item_field*) item->real_item(); 
        DBUG_ASSERT(item->real_item()->type() == Item::FIELD_ITEM);

        /* not doing loose index scan for derived tables */
        if (!item_field->field)
        {
          cause= "derived table";
          goto next_index;
        }

        /* Find the order of the key part in the index. */
        key_part_nr= get_field_keypart(cur_index_info, item_field->field);
        /*
          Check if this attribute was already present in the select list.
          If it was present, then its corresponding key part was alredy used.
        */
        if (used_key_parts_map.is_set(key_part_nr))
          continue;
        if (key_part_nr < 1 ||
            (!is_agg_distinct && key_part_nr > join->fields_list.elements))
        {
          cause= "select attribute not prefix in index";
          goto next_index;
        }
        cur_part= cur_index_info->key_part + key_part_nr - 1;
        cur_group_prefix_len+= cur_part->store_length;
        used_key_parts_map.set_bit(key_part_nr);
        ++cur_group_key_parts;
        max_key_part= MY_MAX(max_key_part,key_part_nr);
      }
      /*
        Check that used key parts forms a prefix of the index.
        To check this we compare bits in all_parts and cur_parts.
        all_parts have all bits set from 0 to (max_key_part-1).
        cur_parts have bits set for only used keyparts.
      */
      ulonglong all_parts, cur_parts;
      all_parts= (1ULL << max_key_part) - 1;
      cur_parts= used_key_parts_map.to_ulonglong() >> 1;
      if (all_parts != cur_parts)
        goto next_index;
    }

    /* Check (SA2). */
    if (min_max_arg_item)
    {
      key_part_nr= get_field_keypart(cur_index_info, min_max_arg_item->field);
      if (key_part_nr <= cur_group_key_parts)
      {
        cause= "aggregate column not suffix in idx";
        goto next_index;
      }
      min_max_arg_part= cur_index_info->key_part + key_part_nr - 1;
    }

    /*
      Aplly a heuristic: there is no point to use loose index scan when we're
      using the whole unique index.
    */
    if (cur_index_info->flags & HA_NOSAME && 
        cur_group_key_parts == cur_index_info->user_defined_key_parts)
    {
      cause= "using unique index";
      goto next_index;
    }

    /*
      Check (NGA1, NGA2) and extract a sequence of constants to be used as part
      of all search keys.
    */

    /*
      If there is MIN/MAX, each keypart between the last group part and the
      MIN/MAX part must participate in one equality with constants, and all
      keyparts after the MIN/MAX part must not be referenced in the query.

      If there is no MIN/MAX, the keyparts after the last group part can be
      referenced only in equalities with constants, and the referenced keyparts
      must form a sequence without any gaps that starts immediately after the
      last group keypart.
    */
    key_parts= table->actual_n_key_parts(cur_index_info);
    last_part= cur_index_info->key_part + key_parts;
    first_non_group_part= (cur_group_key_parts < key_parts) ?
                          cur_index_info->key_part + cur_group_key_parts :
                          NULL;
    first_non_infix_part= min_max_arg_part ?
                          (min_max_arg_part < last_part) ?
                             min_max_arg_part :
                             NULL :
                           NULL;
    if (first_non_group_part &&
        (!min_max_arg_part || (min_max_arg_part - first_non_group_part > 0)))
    {
      if (tree)
      {
        SEL_ARG *index_range_tree= tree->keys[cur_param_idx];
        if (!get_constant_key_infix(cur_index_info, index_range_tree,
                                    first_non_group_part, min_max_arg_part,
                                    last_part, thd, cur_key_infix, 
                                    &cur_key_infix_len,
                                    &first_non_infix_part))
        {
          cause= "nonconst equality gap attribute";
          goto next_index;
        }
      }
      else if (min_max_arg_part &&
               (min_max_arg_part - first_non_group_part > 0))
      {
        /*
          There is a gap but no range tree, thus no predicates at all for the
          non-group keyparts.
        */
        cause= "no nongroup keypart predicate";
        goto next_index;
      }
      else if (first_non_group_part && join->conds)
      {
        /*
          If there is no MIN/MAX function in the query, but some index
          key part is referenced in the WHERE clause, then this index
          cannot be used because the WHERE condition over the keypart's
          field cannot be 'pushed' to the index (because there is no
          range 'tree'), and the WHERE clause must be evaluated before
          GROUP BY/DISTINCT.
        */
        /*
          Store the first and last keyparts that need to be analyzed
          into one array that can be passed as parameter.
        */
        KEY_PART_INFO *key_part_range[2];
        key_part_range[0]= first_non_group_part;
        key_part_range[1]= last_part;

        /* Check if cur_part is referenced in the WHERE clause. */
        if (join->conds->walk(&Item::find_item_in_field_list_processor,
                              key_part_range, WALK_SUBQUERY))
        {
          cause= "keypart reference from where clause";
          goto next_index;
        }
      }
    }

    /*
      Test (WA1) partially - that no other keypart after the last infix part is
      referenced in the query.
    */
    if (first_non_infix_part)
    {
      cur_part= first_non_infix_part +
                (min_max_arg_part && (min_max_arg_part < last_part));
      for (; cur_part != last_part; cur_part++)
      {
        if (bitmap_is_set(table->read_set, cur_part->field->field_index))
        {
          cause= "keypart after infix in query";
          goto next_index;
        }
      }
    }

    /**
      Test WA2:If there are conditions on a column C participating in
      MIN/MAX, those conditions must be conjunctions to all earlier
      keyparts. Otherwise, Loose Index Scan cannot be used.
    */
    if (tree && min_max_arg_item)
    {
      SEL_ARG *index_range_tree= tree->keys[cur_param_idx];
      SEL_ARG *cur_range= NULL;
      if (get_sel_arg_for_keypart(min_max_arg_part->field,
                                  index_range_tree, &cur_range) ||
          (cur_range && cur_range->type != SEL_ARG::KEY_RANGE))
      {
        cause= "minmax keypart in disjunctive query";
        goto next_index;
      }
    }

    /* If we got to this point, cur_index_info passes the test. */
    key_infix_parts= cur_key_infix_len ? (uint) 
                     (first_non_infix_part - first_non_group_part) : 0;
    cur_used_key_parts= cur_group_key_parts + key_infix_parts;

    /* Compute the cost of using this index. */
    if (tree)
    {
      if ((cur_index_tree= tree->keys[cur_param_idx]))
      {
        cur_quick_prefix_records= param->quick_rows[cur_index];
        if (!cur_quick_prefix_records)
        {
          /*
            Non-constant table has a range with rows=0. Can happen e.g. for
            Merge tables. Regular range access will be just as good as loose
            scan.
          */
          if (unlikely(trace_idx.trace_started()))
            trace_idx.add("aborting_search", "range with rows=0");
          DBUG_RETURN(NULL);
        }
        if (unlikely(cur_index_tree && thd->trace_started()))
        {
          Json_writer_array trace_range(thd, "ranges");
          trace_ranges(&trace_range, param, cur_param_idx,
                       cur_index_tree, cur_index_info->key_part);
        }
      }
      else
        cur_quick_prefix_records= HA_POS_ERROR;
    }
    cost_group_min_max(table, cur_index_info, cur_used_key_parts,
                       cur_group_key_parts, tree, cur_index_tree,
                       cur_quick_prefix_records, have_min, have_max,
                       &cur_read_cost, &cur_records);
    /*
      If cur_read_cost is lower than best_read_cost use cur_index.
      Do not compare doubles directly because they may have different
      representations (64 vs. 80 bits).
    */
    trace_idx.add("rows", cur_records).add("cost", cur_read_cost);

    if (cur_read_cost < best_read_cost - (DBL_EPSILON * cur_read_cost))
    {
      index_info= cur_index_info;
      index= cur_index;
      best_read_cost= cur_read_cost;
      best_records= cur_records;
      best_index_tree= cur_index_tree;
      best_quick_prefix_records= cur_quick_prefix_records;
      best_param_idx= cur_param_idx;
      group_key_parts= cur_group_key_parts;
      group_prefix_len= cur_group_prefix_len;
      key_infix_len= cur_key_infix_len;
      if (key_infix_len)
        memcpy (key_infix, cur_key_infix, sizeof (key_infix));
      used_key_parts= cur_used_key_parts;
    }

  next_index:
    if (cause)
    {
      trace_idx.add("usable", false).add("cause", cause);
      cause= NULL;
    }
  }

  trace_indexes.end();

  if (!index_info) /* No usable index found. */
    DBUG_RETURN(NULL);

  /* Check (SA3) for the where clause. */
  bool has_min_max_fld= false, has_other_fld= false;
  if (join->conds && min_max_arg_item &&
      !check_group_min_max_predicates(join->conds, min_max_arg_item,
                                      Field::image_type(index_info->algorithm),
                                      &has_min_max_fld, &has_other_fld))
  {
    if (unlikely(trace_group.trace_started()))
      trace_group.
        add("usable", false).
        add("cause", "unsupported predicate on agg attribute");
    DBUG_RETURN(NULL);
  }

  /*
    Check (SA6) if clustered key is used
  */
  if (is_agg_distinct && table->file->is_clustering_key(index))
  {
    if (unlikely(trace_group.trace_started()))
      trace_group.
        add("usable", false).
        add("cause", "index is clustered");
    DBUG_RETURN(NULL);
  }

  /* The query passes all tests, so construct a new TRP object. */
  read_plan= new (param->mem_root)
                 TRP_GROUP_MIN_MAX(have_min, have_max, is_agg_distinct,
                                   min_max_arg_part,
                                   group_prefix_len, used_key_parts,
                                   group_key_parts, index_info, index,
                                   key_infix_len,
                                   (key_infix_len > 0) ? key_infix : NULL,
                                   tree, best_index_tree, best_param_idx,
                                   best_quick_prefix_records);
  if (read_plan)
  {
    if (tree && read_plan->quick_prefix_records == 0)
      DBUG_RETURN(NULL);

    read_plan->read_cost= best_read_cost;
    read_plan->records=   best_records;
    if (is_agg_distinct)
    {
      double best_cost, duplicate_removal_cost;
      ulonglong records;
      handler *file= table->file;

      /* Calculate cost of distinct scan on index */
      if (best_index_tree && read_plan->quick_prefix_records)
        records=       read_plan->quick_prefix_records;
      else
        records= table->stat_records();

      best_cost= file->cost(file->ha_key_scan_time(index, records));
      /* We only have 'best_records' left after duplication elimination */
      best_cost+= best_records * WHERE_COST_THD(thd);
      duplicate_removal_cost= (DUPLICATE_REMOVAL_COST * records);

      if (best_cost < read_plan->read_cost + duplicate_removal_cost)
      {
        read_plan->read_cost= best_cost;
        read_plan->use_index_scan();
        trace_group.
          add("scan_cost", best_cost).
          add("index_scan", true);
      }
    }

    DBUG_PRINT("info",
               ("Returning group min/max plan: cost: %g, records: %lu",
                read_plan->read_cost, (ulong) read_plan->records));
  }

  DBUG_RETURN(read_plan);
}


/*
  Check that the MIN/MAX attribute participates only in range predicates
  with constants.

  SYNOPSIS
    check_group_min_max_predicates()
    cond            [in]  the expression tree being analyzed
    min_max_arg     [in]  the field referenced by the MIN/MAX function(s)
    image_type      [in]
    has_min_max_arg [out] true if the subtree being analyzed references
                          min_max_arg
    has_other_arg   [out] true if the subtree being analyzed references a
                          column other min_max_arg

  DESCRIPTION
    The function walks recursively over the cond tree representing a WHERE
    clause, and checks condition (SA3) - if a field is referenced by a MIN/MAX
    aggregate function, it is referenced only by one of the following
    predicates $FUNC$:
    {=, !=, <, <=, >, >=, between, is [not] null, multiple equal}.
    In addition the function checks that the WHERE condition is equivalent to
    "cond1 AND cond2" where :
    cond1 - does not use min_max_column at all.
    cond2 - is an AND/OR tree with leaves in form
    "$FUNC$(min_max_column[, const])".

  RETURN
    TRUE  if cond passes the test
    FALSE o/w
*/

static bool
check_group_min_max_predicates(Item *cond, Item_field *min_max_arg_item,
                               Field::imagetype image_type,
                               bool *has_min_max_arg, bool *has_other_arg)
{
  DBUG_ENTER("check_group_min_max_predicates");
  DBUG_ASSERT(cond && min_max_arg_item);

  cond= cond->real_item();
  Item::Type cond_type= cond->real_type();
  if (cond_type == Item::COND_ITEM) /* 'AND' or 'OR' */
  {
    DBUG_PRINT("info", ("Analyzing: %s", ((Item_func*) cond)->func_name()));
    List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
    Item *and_or_arg;
    Item_func::Functype func_type= ((Item_cond*) cond)->functype();
    bool has_min_max= false, has_other= false;
    while ((and_or_arg= li++))
    {
      /*
        The WHERE clause doesn't pass the condition if:
        (1) any subtree doesn't pass the condition or
        (2) the subtree passes the test, but it is an OR and it references both
            the min/max argument and other columns.
      */
      if (!check_group_min_max_predicates(and_or_arg, min_max_arg_item,     //1
                                          image_type,
                                          &has_min_max, &has_other) ||
          (func_type == Item_func::COND_OR_FUNC && has_min_max && has_other))//2
        DBUG_RETURN(FALSE);
    }
    *has_min_max_arg= has_min_max || *has_min_max_arg;
    *has_other_arg= has_other || *has_other_arg;
    DBUG_RETURN(TRUE);
  }

  /*
    Disallow loose index scan if the MIN/MAX argument field is referenced by
    a subquery in the WHERE clause.
  */

  if (unlikely(cond_type == Item::SUBSELECT_ITEM))
  {
    Item_subselect *subs_cond= (Item_subselect*) cond;
    if (subs_cond->is_correlated)
    {
      DBUG_ASSERT(subs_cond->upper_refs.elements > 0);
      List_iterator_fast<Item_subselect::Ref_to_outside>
        li(subs_cond->upper_refs);
      Item_subselect::Ref_to_outside *dep;
      while ((dep= li++))
      {
        if (dep->item->eq(min_max_arg_item, FALSE))
          DBUG_RETURN(FALSE);
      }
    }
    DBUG_RETURN(TRUE);
  }
  /*
    Subquery with IS [NOT] NULL
    TODO: Look into the cache_item and optimize it like we do for
    subselect's above
   */
  if (unlikely(cond_type == Item::CACHE_ITEM))
    DBUG_RETURN(cond->const_item());
  
  /*
    Condition of the form 'field' is equivalent to 'field <> 0' and thus
    satisfies the SA3 condition.
  */
  if (cond_type == Item::FIELD_ITEM)
  {
    DBUG_PRINT("info", ("Analyzing: %s", cond->full_name()));
    if (min_max_arg_item->eq((Item_field*)cond, 1))
      *has_min_max_arg= true;
    else
      *has_other_arg= true;
    DBUG_RETURN(TRUE);
  }

  /* We presume that at this point there are no other Items than functions. */
  DBUG_ASSERT(cond_type == Item::FUNC_ITEM);
  if (unlikely(cond_type != Item::FUNC_ITEM))   /* Safety */
    DBUG_RETURN(FALSE);
  
  /* Test if cond references only group-by or non-group fields. */
  Item_func *pred= (Item_func*) cond;
  Item_func::Functype pred_type= pred->functype();
  DBUG_PRINT("info", ("Analyzing: %s", pred->func_name()));
  if (pred_type == Item_func::MULT_EQUAL_FUNC)
  {
    /*
      Check that each field in a multiple equality is either a constant or
      it is a reference to the min/max argument, or it doesn't contain the
      min/max argument at all.
    */
    Item_equal_fields_iterator eq_it(*((Item_equal*)pred));
    Item *eq_item;
    bool has_min_max= false, has_other= false;
    while ((eq_item= eq_it++))
    {
      if (min_max_arg_item->eq(eq_item->real_item(), 1))
        has_min_max= true;
      else
        has_other= true;
    }
    *has_min_max_arg= has_min_max || *has_min_max_arg;
    *has_other_arg= has_other || *has_other_arg;
    DBUG_RETURN(!(has_min_max && has_other));
  }

  Item **arguments= pred->arguments();
  Item *cur_arg;
  bool has_min_max= false, has_other= false;
  for (uint arg_idx= 0; arg_idx < pred->argument_count (); arg_idx++)
  {
    cur_arg= arguments[arg_idx]->real_item();
    DBUG_PRINT("info", ("cur_arg: %s", cur_arg->full_name()));
    if (cur_arg->type() == Item::FIELD_ITEM)
    {
      if (min_max_arg_item->eq(cur_arg, 1)) 
      {
        has_min_max= true;
        /*
          If pred references the MIN/MAX argument, check whether pred is a range
          condition that compares the MIN/MAX argument with a constant.
        */
        if (pred_type != Item_func::EQUAL_FUNC     &&
            pred_type != Item_func::LT_FUNC        &&
            pred_type != Item_func::LE_FUNC        &&
            pred_type != Item_func::GT_FUNC        &&
            pred_type != Item_func::GE_FUNC        &&
            pred_type != Item_func::BETWEEN        &&
            pred_type != Item_func::ISNULL_FUNC    &&
            pred_type != Item_func::ISNOTNULL_FUNC &&
            pred_type != Item_func::EQ_FUNC        &&
            pred_type != Item_func::NE_FUNC)
          DBUG_RETURN(FALSE);

        /* Check that pred compares min_max_arg_item with a constant. */
        Item *args[3];
        bzero(args, 3 * sizeof(Item*));
        bool inv;
        /* Test if this is a comparison of a field and a constant. */
        if (!simple_pred(pred, args, &inv))
          DBUG_RETURN(FALSE);

        /*
          Follow the logic in Item_func_ne::get_func_mm_tree(): condition
          in form "tbl.primary_key <> const" is not used to produce intervals.

          If the condition doesn't have an equivalent interval, this means we
          fail LooseScan's condition SA3. Return FALSE to indicate this.
        */
        if (pred_type == Item_func::NE_FUNC &&
            is_field_an_unique_index(min_max_arg_item->field))
          DBUG_RETURN(FALSE);

        if (args[0] && args[1]) // this is a binary function or BETWEEN
        {
          DBUG_ASSERT(pred->fixed_type_handler());
          DBUG_ASSERT(pred->fixed_type_handler()->is_bool_type());
          Item_bool_func *bool_func= (Item_bool_func*) pred;
          Field *field= min_max_arg_item->field;
          if (!args[2]) // this is a binary function
          {
            if (field->can_optimize_group_min_max(bool_func, args[1]) !=
                Data_type_compatibility::OK)
              DBUG_RETURN(FALSE);
          }
          else // this is BETWEEN
          {
            if (field->can_optimize_group_min_max(bool_func, args[1]) !=
                Data_type_compatibility::OK ||
                field->can_optimize_group_min_max(bool_func, args[2]) !=
                Data_type_compatibility::OK)
              DBUG_RETURN(FALSE);
          }
        }
      }
      else
        has_other= true;
    }
    else if (cur_arg->type() == Item::FUNC_ITEM)
    {
      if (!check_group_min_max_predicates(cur_arg, min_max_arg_item, image_type,
                                          &has_min_max, &has_other))
        DBUG_RETURN(FALSE);
    }
    else if (cur_arg->can_eval_in_optimize())
    {
      /*
        For predicates of the form "const OP expr" we also have to check 'expr'
        to make a decision.
      */
      continue;
    }
    else
      DBUG_RETURN(FALSE);
    if(has_min_max && has_other)
      DBUG_RETURN(FALSE);
  }
  *has_min_max_arg= has_min_max || *has_min_max_arg;
  *has_other_arg= has_other || *has_other_arg;

  DBUG_RETURN(TRUE);
}


/*
  Get the SEL_ARG tree 'tree' for the keypart covering 'field', if
  any. 'tree' must be a unique conjunction to ALL predicates in earlier
  keyparts of 'keypart_tree'.

  E.g., if 'keypart_tree' is for a composite index (kp1,kp2) and kp2
  covers 'field', all these conditions satisfies the requirement:

   1. "(kp1=2 OR kp1=3) AND kp2=10"    => returns "kp2=10"
   2. "(kp1=2 AND kp2=10) OR (kp1=3 AND kp2=10)"  => returns "kp2=10"
   3. "(kp1=2 AND (kp2=10 OR kp2=11)) OR (kp1=3 AND (kp2=10 OR kp2=11))"
                                       => returns "kp2=10  OR kp2=11"

   whereas these do not
   1. "(kp1=2 AND kp2=10) OR kp1=3"
   2. "(kp1=2 AND kp2=10) OR (kp1=3 AND kp2=11)"
   3. "(kp1=2 AND kp2=10) OR (kp1=3 AND (kp2=10 OR kp2=11))"

   This function effectively tests requirement WA2. In combination with
   a test that the returned tree has no more than one range it is also
   a test of NGA3.

  @param[in]   field          The field we want the SEL_ARG tree for
  @param[in]   keypart_tree   Root node of the SEL_ARG* tree for the index
  @param[out]  cur_range      The SEL_ARG tree, if any, for the keypart
                              covering field 'keypart_field'
  @retval true   'keypart_tree' contained a predicate for 'field' that
                  is not conjunction to all predicates on earlier keyparts
  @retval false  otherwise
*/

static bool
get_sel_arg_for_keypart(Field *field,
                        SEL_ARG *keypart_tree,
                        SEL_ARG **cur_range)
{
  if (keypart_tree == NULL)
    return false;
  if (keypart_tree->field->eq(field))
  {
    *cur_range= keypart_tree;
    return false;
  }

  SEL_ARG *tree_first_range= NULL;
  SEL_ARG *first_kp=  keypart_tree->first();

  for (SEL_ARG *cur_kp= first_kp; cur_kp; cur_kp= cur_kp->next)
  {
    SEL_ARG *curr_tree= NULL;
    if (cur_kp->next_key_part)
    {
      if (get_sel_arg_for_keypart(field,
                                  cur_kp->next_key_part,
                                  &curr_tree))
        return true;
    }
    /*
      Check if the SEL_ARG tree for 'field' is identical for all ranges in
      'keypart_tree
     */
    if (cur_kp == first_kp)
      tree_first_range= curr_tree;
    else if (!all_same(tree_first_range, curr_tree))
      return true;
  }
  *cur_range= tree_first_range;
  return false;
}

/*
  Extract a sequence of constants from a conjunction of equality predicates.

  SYNOPSIS
    get_constant_key_infix()
    index_info             [in]  Descriptor of the chosen index.
    index_range_tree       [in]  Range tree for the chosen index
    first_non_group_part   [in]  First index part after group attribute parts
    min_max_arg_part       [in]  The keypart of the MIN/MAX argument if any
    last_part              [in]  Last keypart of the index
    thd                    [in]  Current thread
    key_infix              [out] Infix of constants to be used for index lookup
    key_infix_len          [out] Length of the infix
    first_non_infix_part   [out] The first keypart after the infix (if any)

  DESCRIPTION
    Test conditions (NGA1, NGA2, NGA3) from get_best_group_min_max(). Namely,
    for each keypart field NG_i not in GROUP-BY, check that there is exactly one
    constant equality predicate among conds with the form (NG_i = const_ci) or
    (const_ci = NG_i).. In addition, there can only be one range when there is
    such a gap.
    Thus all the NGF_i attributes must fill the 'gap' between the last group-by
    attribute and the MIN/MAX attribute in the index (if present).  Also ensure
    that there is only a single range on NGF_i (NGA3). If these
    conditions hold, copy each constant from its corresponding predicate into
    key_infix, in the order its NG_i attribute appears in the index, and update
    key_infix_len with the total length of the key parts in key_infix.

  RETURN
    TRUE  if the index passes the test
    FALSE o/w
*/
static bool
get_constant_key_infix(KEY *index_info, SEL_ARG *index_range_tree,
                       KEY_PART_INFO *first_non_group_part,
                       KEY_PART_INFO *min_max_arg_part,
                       KEY_PART_INFO *last_part, THD *thd,
                       uchar *key_infix, uint *key_infix_len,
                       KEY_PART_INFO **first_non_infix_part)
{
  KEY_PART_INFO *cur_part;
  /* End part for the first loop below. */
  KEY_PART_INFO *end_part= min_max_arg_part ? min_max_arg_part : last_part;

  *key_infix_len= 0;
  uchar *key_ptr= key_infix;
  for (cur_part= first_non_group_part; cur_part != end_part; cur_part++)
  {
    SEL_ARG *cur_range= NULL;
    /*
      Check NGA3:
      1. get_sel_arg_for_keypart gets the range tree for the 'field' and also
         checks for a unique conjunction of this tree with all the predicates
         on the earlier keyparts in the index.
      2. Check for multiple ranges on the found keypart tree.

      We assume that index_range_tree points to the leftmost keypart in
      the index.
    */
    if (get_sel_arg_for_keypart(cur_part->field, index_range_tree,
                                &cur_range))
      return false;

    if (cur_range && cur_range->elements > 1)
      return false;

    if (!cur_range || cur_range->type != SEL_ARG::KEY_RANGE)
    {
      if (min_max_arg_part)
        return false; /* The current keypart has no range predicates at all. */
      else
      {
        *first_non_infix_part= cur_part;
        return true;
      }
    }

    if ((cur_range->min_flag & NO_MIN_RANGE) ||
        (cur_range->max_flag & NO_MAX_RANGE) ||
        (cur_range->min_flag & NEAR_MIN) || (cur_range->max_flag & NEAR_MAX))
      return false;

    uint field_length= cur_part->store_length;
    if (cur_range->maybe_null &&
         cur_range->min_value[0] && cur_range->max_value[0])
    {
      /*
        cur_range specifies 'IS NULL'. In this case the argument points
        to a "null value" (is_null_string) that may not always be long
        enough for a direct memcpy to a field.
      */
      DBUG_ASSERT (field_length > 0);
      *key_ptr= 1;
      bzero(key_ptr+1,field_length-1);
      key_ptr+= field_length;
      *key_infix_len+= field_length;
    }
    else if (memcmp(cur_range->min_value, cur_range->max_value, field_length) == 0)
    { /* cur_range specifies an equality condition. */
      memcpy(key_ptr, cur_range->min_value, field_length);
      key_ptr+= field_length;
      *key_infix_len+= field_length;
    }
    else
      return false;
  }

  if (!min_max_arg_part && (cur_part == last_part))
    *first_non_infix_part= last_part;

  return TRUE;
}


/*
  Find the key part referenced by a field.

  SYNOPSIS
    get_field_keypart()
    index  descriptor of an index
    field  field that possibly references some key part in index

  NOTES
    The return value can be used to get a KEY_PART_INFO pointer by
    part= index->key_part + get_field_keypart(...) - 1;

  RETURN
    Positive number which is the consecutive number of the key part, or
    0 if field does not reference any index field.
*/

static inline uint
get_field_keypart(KEY *index, Field *field)
{
  KEY_PART_INFO *part, *end;

  for (part= index->key_part,
         end= part + field->table->actual_n_key_parts(index);
       part < end; part++)
  {
    if (field->eq(part->field))
      return (uint)(part - index->key_part + 1);
  }
  return 0;
}


/*
  Compute the cost of a quick_group_min_max_select for a particular index.

  SYNOPSIS
    cost_group_min_max()
    table                [in] The table being accessed
    index_info           [in] The index used to access the table
    used_key_parts       [in] Number of key parts used to access the index
    group_key_parts      [in] Number of index key parts in the group prefix
    range_tree           [in] Tree of ranges for all indexes
    index_tree           [in] The range tree for the current index
    quick_prefix_records [in] Number of records retrieved by the internally
			      used quick range select if any
    have_min             [in] True if there is a MIN function
    have_max             [in] True if there is a MAX function
    read_cost           [out] The cost to retrieve rows via this quick select
    out_records         [out] The number of rows retrieved

  DESCRIPTION
    This method computes the access cost of a TRP_GROUP_MIN_MAX instance and
    the number of rows returned.

    The used algorithm used for finding the rows is:

    For each range (if no ranges, the range is the whole table)
      Do an index search for the start of the range
      As long as the found key is withing the range
        If the found row matches the where clause, use the row otherwise skip it
        Scan index for next group, jumping over all identical keys, done in
        QUICK_GROUP_MIN_MAX_SELECT::next_prefix
        If the engine does not support a native next_prefix, we will
        either scan the index for the next value or do a new index dive
        with 'find next bigger key'.

    When using MIN() and MAX() in the query, the calls to the storage engine
    are as follows for each group:
      Assuming kp1 in ('abc','def','ghi)' and kp2 between 1000 and 2000

      read_key('abc', HA_READ_KEY_OR_NEXT)
      In case of MIN() we do:
        read_key('abc,:'1000', HA_READ_KEY_OR_NEXT)
      In case of MAX() we do
        read_key('abc,:'2000', HA_READ_PREFIX_LAST_OR_PREV)
      In the following code we will assume that the MIN key will be in
      the same block as the first key read.
      (We should try to optimize away the extra call for MAX() at some
       point).

  NOTES
    See get_best_group_min_max() for which kind of queries this function
    will be called.

    The cost computation distinguishes several cases:
    1) No equality predicates over non-group attributes (thus no key_infix).
       If groups are bigger than blocks on the average, then we assume that it
       is very unlikely that block ends are aligned with group ends, thus even
       if we look for both MIN and MAX keys, all pairs of neighbor MIN/MAX
       keys, except for the first MIN and the last MAX keys, will be in the
       same block.  If groups are smaller than blocks, then we are going to
       read all blocks.
    2) There are equality predicates over non-group attributes.
       In this case the group prefix is extended by additional constants, and
       as a result the min/max values are inside sub-groups of the original
       groups. The number of blocks that will be read depends on whether the
       ends of these sub-groups will be contained in the same or in different
       blocks. We compute the probability for the two ends of a subgroup to be
       in two different blocks as the ratio of:
       - the number of positions of the left-end of a subgroup inside a group,
         such that the right end of the subgroup is past the end of the buffer
         containing the left-end, and
       - the total number of possible positions for the left-end of the
         subgroup, which is the number of keys in the containing group.
       We assume it is very unlikely that two ends of subsequent subgroups are
       in the same block.
    3) The are range predicates over the group attributes.
       Then some groups may be filtered by the range predicates. We use the
       selectivity of the range predicates to decide how many groups will be
       filtered.

  TODO
     - Take into account the optional range predicates over the MIN/MAX
       argument.
     - Check if we have a PK index and we use all cols - then each key is a
       group, and it will be better to use an index scan.

  RETURN
    None
*/

void cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
                        uint group_key_parts, SEL_TREE *range_tree,
                        SEL_ARG *index_tree, ha_rows quick_prefix_records,
                        bool have_min, bool have_max,
                        double *read_cost, ha_rows *out_records)
{
  uint    key_length;
  ha_rows records;
  ha_rows num_groups;
  ha_rows num_blocks;
  ha_rows keys_per_group;
  double quick_prefix_selectivity;
  ulonglong io_cost;
  handler *file= table->file;
  DBUG_ENTER("cost_group_min_max");

  /* Same code as in handler::key_read_time() */
  records= table->stat_records();
  key_length= (index_info->key_length + file->ref_length);

  /* Compute the number of keys in a group. */
  if (!group_key_parts)
  {
    /* Summary over the whole table */
    keys_per_group= MY_MAX(records,1);
  }
  else
  {
    keys_per_group= (ha_rows) index_info->actual_rec_per_key(group_key_parts -
                                                             1);
    if (keys_per_group == 0) /* If there is no statistics try to guess */
    {
      /* each group contains 10% of all records */
      keys_per_group= (records / 10) + 1;
    }
  }
  if (keys_per_group > 1)
    num_groups= (records / keys_per_group) + 1;
  else
    num_groups= records;

  DBUG_ASSERT(keys_per_group > 0);
  DBUG_ASSERT(num_groups > 0);

  /* Apply the selectivity of the quick select for group prefixes. */
  if (range_tree && (quick_prefix_records != HA_POS_ERROR))
  {
    int groups;
    quick_prefix_selectivity= (double) quick_prefix_records /
                              (double) records;
    num_groups= (ha_rows) rint(num_groups * quick_prefix_selectivity);
    records= quick_prefix_records;

    /*
      Try to handle cases like
      WHERE a in (1,2,3) GROUP BY a

      If all ranges are eq_ranges for the group_key_parts we can use
      this as the number of groups.
    */
    groups= index_tree->number_of_eq_groups(group_key_parts);
    if (groups > 0)
      num_groups= groups;
    else
    {
      /*
        Expect at least as many groups as there is ranges in the index

        This is mostly relevant for queries with few records, which is
        something we have a lot of in our test suites.
        In theory it is possible to scan the index_tree and for cases
        where all ranges are eq ranges, we could calculate the exact number
        of groups. This is probably an overkill so for now we estimate
        the lower level of number of groups by the range elements in the
        tree.
      */
      set_if_bigger(num_groups, MY_MAX(index_tree->elements, 1));
    }
    /* There cannot be more groups than matched records */
    set_if_smaller(num_groups, quick_prefix_records);
  }
  DBUG_ASSERT(num_groups <= records);

  /* Calculate the number of blocks we will touch for the table or range scan */
  num_blocks= (records * key_length / INDEX_BLOCK_FILL_FACTOR_DIV *
               INDEX_BLOCK_FILL_FACTOR_MUL) / file->stats.block_size + 1;

  io_cost= (have_max) ? num_groups * 2 : num_groups;
  set_if_smaller(io_cost, num_blocks);

  /*
    CPU cost must be comparable to that of an index scan as computed
    in SQL_SELECT::test_quick_select(). When the groups are small,
    e.g. for a unique index, using index scan will be cheaper since it
    reads the next record without having to re-position to it on every
    group.
  */
  uint keyno= (uint) (index_info - table->key_info);
  *read_cost= file->cost(file->ha_keyread_and_compare_time(keyno,
                                                           (ulong) num_groups,
                                                           num_groups,
                                                           io_cost));
  *out_records= num_groups;

  DBUG_PRINT("info",
             ("rows: %lu  keys/group: %lu  "
              "result rows: %lu  blocks: %lu",
              (ulong) records, (ulong) keys_per_group,
              (ulong) *out_records, (ulong) num_blocks));
  DBUG_VOID_RETURN;
}


/*
  Construct a new quick select object for queries with group by with min/max.

  SYNOPSIS
    TRP_GROUP_MIN_MAX::make_quick()
    param              Parameter from test_quick_select
    retrieve_full_rows ignored
    parent_alloc       Memory pool to use, if any.

  NOTES
    Make_quick ignores the retrieve_full_rows parameter because
    QUICK_GROUP_MIN_MAX_SELECT always performs 'index only' scans.
    The other parameter are ignored as well because all necessary
    data to create the QUICK object is computed at this TRP creation
    time.

  RETURN
    New QUICK_GROUP_MIN_MAX_SELECT object if successfully created,
    NULL otherwise.
*/

QUICK_SELECT_I *
TRP_GROUP_MIN_MAX::make_quick(PARAM *param, bool retrieve_full_rows,
                              MEM_ROOT *parent_alloc)
{
  QUICK_GROUP_MIN_MAX_SELECT *quick;
  DBUG_ENTER("TRP_GROUP_MIN_MAX::make_quick");

  quick= new QUICK_GROUP_MIN_MAX_SELECT(param->table,
                                        param->thd->lex->current_select->join,
                                        have_min, have_max, 
                                        have_agg_distinct, min_max_arg_part,
                                        group_prefix_len, group_key_parts,
                                        used_key_parts, index_info, index,
                                        read_cost, records, key_infix_len,
                                        key_infix, parent_alloc,
                                        is_index_scan);
  if (!quick)
    DBUG_RETURN(NULL);

  if (quick->init())
  {
    delete quick;
    DBUG_RETURN(NULL);
  }

  if (range_tree)
  {
    DBUG_ASSERT(quick_prefix_records > 0);
    if (quick_prefix_records == HA_POS_ERROR)
      quick->quick_prefix_select= NULL; /* Can't construct a quick select. */
    else
      /* Make a QUICK_RANGE_SELECT to be used for group prefix retrieval. */
      quick->quick_prefix_select= get_quick_select(param, param_idx,
                                                   index_tree,
                                                   HA_MRR_USE_DEFAULT_IMPL, 0,
                                                   &quick->alloc);

    /*
      Extract the SEL_ARG subtree that contains only ranges for the MIN/MAX
      attribute, and create an array of QUICK_RANGES to be used by the
      new quick select.
    */
    if (min_max_arg_part)
    {
      SEL_ARG *min_max_range= index_tree;
      while (min_max_range) /* Find the tree for the MIN/MAX key part. */
      {
        if (min_max_range->field->eq(min_max_arg_part->field))
          break;
        min_max_range= min_max_range->next_key_part;
      }
      /* Scroll to the leftmost interval for the MIN/MAX argument. */
      while (min_max_range && min_max_range->prev)
        min_max_range= min_max_range->prev;
      /* Create an array of QUICK_RANGEs for the MIN/MAX argument. */
      while (min_max_range)
      {
        if (quick->add_range(min_max_range))
        {
          delete quick;
          quick= NULL;
          DBUG_RETURN(NULL);
        }
        min_max_range= min_max_range->next;
      }
    }
  }
  else
    quick->quick_prefix_select= NULL;

  quick->update_key_stat();
  quick->adjust_prefix_ranges();

  DBUG_RETURN(quick);
}


/*
  @brief
    Return true if the select is using "Using index for group-by" and also
    has "ORDER BY ... FETCH FIRST n ROWS WITH TIES"

  @detail
    There is a rewrite that removes the ORDER BY (JOIN::order) if the select
    also has a GROUP BY that produces a compatible ordering.
    However "FETCH FIRST ... WITH TIES" needs an ORDER BY clause (in
    JOIN::alloc_order_fields()).
    GROUP BY strategies handle it this way:
    - For strategies using temporary table, JOIN::make_aggr_tables_info() will
      put the ORDER BY clause back.
    - OrderedGroupBy in end_send_group() handles WITH TIES with the GROUP BY
      clause (note that SQL doesn't allow "GROUP BY ... WITH TIES").
    - The remaining strategy is QUICK_GROUP_MIN_MAX_SELECT, for which
       = the grouping strategy in the quick select doesn't handle WITH TIES.
       = end_send() would not handle WITH TIES, because JOIN::order is removed.

    The solution is to NOT remove ORDER BY when QUICK_GROUP_MIN_MAX_SELECT is
    used.

    Unfortunately, the optimizer then will not recognize that it can skip
    sorting and will use filesort, which will prevent short-cutting the
    execution when LIMIT is reached.
*/

bool using_with_ties_and_group_min_max(JOIN *join)
{
  if (join->unit->lim.is_with_ties())
  {
    JOIN_TAB *tab= &join->join_tab[join->const_tables];
    if (tab->select && tab->select->quick &&
        tab->select->quick->get_type() ==
          QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
    return true;
  }
  return false;
}

/*
  Construct new quick select for group queries with min/max.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::QUICK_GROUP_MIN_MAX_SELECT()
    table             The table being accessed
    join              Descriptor of the current query
    have_min          TRUE if the query selects a MIN function
    have_max          TRUE if the query selects a MAX function
    min_max_arg_part  The only argument field of all MIN/MAX functions
    group_prefix_len  Length of all key parts in the group prefix
    prefix_key_parts  All key parts in the group prefix
    index_info        The index chosen for data access
    use_index         The id of index_info
    read_cost         Cost of this access method
    records           Number of records returned
    key_infix_len     Length of the key infix appended to the group prefix
    key_infix         Infix of constants from equality predicates
    parent_alloc      Memory pool for this and quick_prefix_select data
    is_index_scan     get the next different key not by jumping on it via
                      index read, but by scanning until the end of the 
                      rows with equal key value.

  RETURN
    None
*/

QUICK_GROUP_MIN_MAX_SELECT::
QUICK_GROUP_MIN_MAX_SELECT(TABLE *table, JOIN *join_arg, bool have_min_arg,
                           bool have_max_arg, bool have_agg_distinct_arg,
                           KEY_PART_INFO *min_max_arg_part_arg,
                           uint group_prefix_len_arg, uint group_key_parts_arg,
                           uint used_key_parts_arg, KEY *index_info_arg,
                           uint use_index, double read_cost_arg,
                           ha_rows records_arg, uint key_infix_len_arg,
                           uchar *key_infix_arg, MEM_ROOT *parent_alloc,
                           bool is_index_scan_arg)
  :file(table->file), join(join_arg), index_info(index_info_arg),
   group_prefix_len(group_prefix_len_arg),
   group_key_parts(group_key_parts_arg), have_min(have_min_arg),
   have_max(have_max_arg), have_agg_distinct(have_agg_distinct_arg),
   seen_first_key(FALSE), min_max_arg_part(min_max_arg_part_arg),
   key_infix(key_infix_arg), key_infix_len(key_infix_len_arg),
   min_functions_it(NULL), max_functions_it(NULL),
   is_index_scan(is_index_scan_arg)
{
  head=       table;
  index=      use_index;
  record=     head->record[0];
  tmp_record= head->record[1];
  read_time= read_cost_arg;
  records= records_arg;
  used_key_parts= used_key_parts_arg;
  real_key_parts= used_key_parts_arg;
  real_prefix_len= group_prefix_len + key_infix_len;
  group_prefix= NULL;
  min_max_arg_len= min_max_arg_part ? min_max_arg_part->store_length : 0;

  /*
    We can't have parent_alloc set as the init function can't handle this case
    yet.
  */
  DBUG_ASSERT(!parent_alloc);
  if (!parent_alloc)
  {
    THD *thd= join->thd;
    init_sql_alloc(key_memory_quick_range_select_root, &alloc,
                   thd->variables.range_alloc_block_size, 0, MYF(MY_THREAD_SPECIFIC));
    thd->mem_root= &alloc;
  }
  else
    bzero(&alloc, sizeof(MEM_ROOT));            // ensure that it's not used
}


/*
  Do post-constructor initialization.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::init()
  
  DESCRIPTION
    The method performs initialization that cannot be done in the constructor
    such as memory allocations that may fail. It allocates memory for the
    group prefix and inifix buffers, and for the lists of MIN/MAX item to be
    updated during execution.

  RETURN
    0      OK
    other  Error code
*/

int QUICK_GROUP_MIN_MAX_SELECT::init()
{
  if (group_prefix) /* Already initialized. */
    return 0;
  /*
    We may use group_prefix to store keys with all select fields, so allocate
    enough space for it.
    We allocate one byte more to serve the case when the last field in
    the buffer is compared using uint3korr (e.g. a Field_newdate field)
  */
  if (!(group_prefix= (uchar*) alloc_root(&alloc,
                                          real_prefix_len+min_max_arg_len+1)))
    return 1;

  if (key_infix_len > 0)
  {
    /*
      The memory location pointed to by key_infix will be deleted soon, so
      allocate a new buffer and copy the key_infix into it.
    */
    uchar *tmp_key_infix= (uchar*) alloc_root(&alloc, key_infix_len);
    if (!tmp_key_infix)
      return 1;
    memcpy(tmp_key_infix, this->key_infix, key_infix_len);
    this->key_infix= tmp_key_infix;
  }

  if (min_max_arg_part)
  {
    if (my_init_dynamic_array(PSI_INSTRUMENT_ME, &min_max_ranges,
                              sizeof(QUICK_RANGE*), 16, 16,
                              MYF(MY_THREAD_SPECIFIC)))
      return 1;

    if (have_min)
    {
      if (!(min_functions= new List<Item_sum>))
        return 1;
    }
    else
      min_functions= NULL;
    if (have_max)
    {
      if (!(max_functions= new List<Item_sum>))
        return 1;
    }
    else
      max_functions= NULL;

    Item_sum *min_max_item;
    Item_sum **func_ptr= join->sum_funcs;
    while ((min_max_item= *(func_ptr++)))
    {
      if (have_min && (min_max_item->sum_func() == Item_sum::MIN_FUNC))
        min_functions->push_back(min_max_item);
      else if (have_max && (min_max_item->sum_func() == Item_sum::MAX_FUNC))
        max_functions->push_back(min_max_item);
    }

    if (have_min)
    {
      if (!(min_functions_it= new List_iterator<Item_sum>(*min_functions)))
        return 1;
    }

    if (have_max)
    {
      if (!(max_functions_it= new List_iterator<Item_sum>(*max_functions)))
        return 1;
    }
  }
  else
    min_max_ranges.elements= 0;

  return 0;
}


QUICK_GROUP_MIN_MAX_SELECT::~QUICK_GROUP_MIN_MAX_SELECT()
{
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::~QUICK_GROUP_MIN_MAX_SELECT");
  if (file->inited != handler::NONE) 
  {
    DBUG_ASSERT(file == head->file);
    head->file->ha_end_keyread();
    /*
      There may be a code path when the same table was first accessed by index,
      then the index is closed, and the table is scanned (order by + loose scan).
    */
    file->ha_index_or_rnd_end();
  }
  if (min_max_arg_part)
    delete_dynamic(&min_max_ranges);
  free_root(&alloc,MYF(0));
  delete min_functions_it;
  delete max_functions_it;
  delete quick_prefix_select;
  DBUG_VOID_RETURN; 
}


/*
  Eventually create and add a new quick range object.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::add_range()
    sel_range  Range object from which a 

  NOTES
    Construct a new QUICK_RANGE object from a SEL_ARG object, and
    add it to the array min_max_ranges. If sel_arg is an infinite
    range, e.g. (x < 5 or x > 4), then skip it and do not construct
    a quick range.

  RETURN
    FALSE on success
    TRUE  otherwise
*/

bool QUICK_GROUP_MIN_MAX_SELECT::add_range(SEL_ARG *sel_range)
{
  QUICK_RANGE *range;
  uint range_flag= sel_range->min_flag | sel_range->max_flag;

  /* Skip (-inf,+inf) ranges, e.g. (x < 5 or x > 4). */
  if ((range_flag & NO_MIN_RANGE) && (range_flag & NO_MAX_RANGE))
    return FALSE;

  if (!(sel_range->min_flag & NO_MIN_RANGE) &&
      !(sel_range->max_flag & NO_MAX_RANGE))
  {
    if (sel_range->maybe_null &&
        sel_range->min_value[0] && sel_range->max_value[0])
      range_flag|= NULL_RANGE; /* IS NULL condition */
    else if (memcmp(sel_range->min_value, sel_range->max_value,
                    min_max_arg_len) == 0)
      range_flag|= EQ_RANGE;  /* equality condition */
  }
  range= new QUICK_RANGE(join->thd, sel_range->min_value, min_max_arg_len,
                         make_keypart_map(sel_range->part),
                         sel_range->max_value, min_max_arg_len,
                         make_keypart_map(sel_range->part),
                         range_flag);
  if (!range)
    return TRUE;
  if (insert_dynamic(&min_max_ranges, (uchar*)&range))
    return TRUE;
  return FALSE;
}


/*
  Opens the ranges if there are more conditions in quick_prefix_select than
  the ones used for jumping through the prefixes.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::adjust_prefix_ranges()

  NOTES
    quick_prefix_select is made over the conditions on the whole key.
    It defines a number of ranges of length x. 
    However when jumping through the prefixes we use only the first 
    few most significant keyparts in the range key. However if there
    are more keyparts to follow the ones we are using we must make the 
    condition on the key inclusive (because x < "ab" means 
    x[0] < 'a' OR (x[0] == 'a' AND x[1] < 'b').
    To achieve the above we must turn off the NEAR_MIN/NEAR_MAX
*/
void QUICK_GROUP_MIN_MAX_SELECT::adjust_prefix_ranges ()
{
  if (quick_prefix_select &&
      group_prefix_len < quick_prefix_select->max_used_key_length)
  {
    DYNAMIC_ARRAY *arr;
    uint inx;

    for (inx= 0, arr= &quick_prefix_select->ranges; inx < arr->elements; inx++)
    {
      QUICK_RANGE *range;

      get_dynamic(arr, (uchar*)&range, inx);
      range->flag &= ~(NEAR_MIN | NEAR_MAX);
    }
  }
}


/*
  Determine the total number and length of the keys that will be used for
  index lookup.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::update_key_stat()

  DESCRIPTION
    The total length of the keys used for index lookup depends on whether
    there are any predicates referencing the min/max argument, and/or if
    the min/max argument field can be NULL.
    This function does an optimistic analysis whether the search key might
    be extended by a constant for the min/max keypart. It is 'optimistic'
    because during actual execution it may happen that a particular range
    is skipped, and then a shorter key will be used. However this is data
    dependent and can't be easily estimated here.

  RETURN
    None
*/

void QUICK_GROUP_MIN_MAX_SELECT::update_key_stat()
{
  max_used_key_length= real_prefix_len;
  if (min_max_ranges.elements > 0)
  {
    QUICK_RANGE *cur_range;
    if (have_min)
    { /* Check if the right-most range has a lower boundary. */
      get_dynamic(&min_max_ranges, (uchar*)&cur_range,
                  min_max_ranges.elements - 1);
      if (!(cur_range->flag & NO_MIN_RANGE))
      {
        max_used_key_length+= min_max_arg_len;
        used_key_parts++;
        return;
      }
    }
    if (have_max)
    { /* Check if the left-most range has an upper boundary. */
      get_dynamic(&min_max_ranges, (uchar*)&cur_range, 0);
      if (!(cur_range->flag & NO_MAX_RANGE))
      {
        max_used_key_length+= min_max_arg_len;
        used_key_parts++;
        return;
      }
    }
  }
  else if (have_min && min_max_arg_part &&
           min_max_arg_part->field->real_maybe_null())
  {
    /*
      If a MIN/MAX argument value is NULL, we can quickly determine
      that we're in the beginning of the next group, because NULLs
      are always < any other value. This allows us to quickly
      determine the end of the current group and jump to the next
      group (see next_min()) and thus effectively increases the
      usable key length.
    */
    max_used_key_length+= min_max_arg_len;
    used_key_parts++;
  }
}


/*
  Initialize a quick group min/max select for key retrieval.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::reset()

  DESCRIPTION
    Initialize the index chosen for access.

  RETURN
    0      OK
    other  Error code
*/

int QUICK_GROUP_MIN_MAX_SELECT::reset(void)
{
  int result;
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::reset");

  seen_first_key= FALSE;
  if (!head->file->keyread_enabled())
    head->file->ha_start_keyread(index); /* We need only the key attributes */

  if ((result= file->ha_index_init(index,1)))
  {
    head->file->print_error(result, MYF(0));
    DBUG_RETURN(result);
  }
  if (quick_prefix_select && quick_prefix_select->reset())
    DBUG_RETURN(1);
  DBUG_RETURN(0);
}



/* 
  Get the next key containing the MIN and/or MAX key for the next group.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::get_next()

  DESCRIPTION
    The method finds the next subsequent group of records that satisfies the
    query conditions and finds the keys that contain the MIN/MAX values for
    the key part referenced by the MIN/MAX function(s). Once a group and its
    MIN/MAX values are found, store these values in the Item_sum objects for
    the MIN/MAX functions. The rest of the values in the result row are stored
    in the Item_field::result_field of each select field. If the query does
    not contain MIN and/or MAX functions, then the function only finds the
    group prefix, which is a query answer itself.

  NOTES
    If both MIN and MAX are computed, then we use the fact that if there is
    no FIRST key (MIN with ASC index or MAX with DESC index), there
    can't be a LAST key (MAX with ASC index or MIN with DESC index) as
    well, so we can skip looking for a LAST key in this case.

  RETURN
    0                  on success
    HA_ERR_END_OF_FILE if returned all keys
    other              if some error occurred
*/

int QUICK_GROUP_MIN_MAX_SELECT::get_next()
{
  int first_res= 0;
  int last_res= 0;
  /*
    reverse: whether the min/max arg has reverse index. If there's no
    min nor max its value is irrelevant and unused but we assign it
    false anyway.
  */
  DBUG_ASSERT(!min_max_arg_part || have_min || have_max);
  bool reverse= min_max_arg_part != NULL &&
    (min_max_arg_part->key_part_flag & HA_REVERSE_SORT);
  bool have_first= reverse ? have_max : have_min;
  bool have_last= reverse ? have_min : have_max;
#ifdef HPUX11
  /*
    volatile is required by a bug in the HP compiler due to which the
    last test of result fails.
  */
  volatile int result;
#else
  int result;
#endif
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::get_next");

  /*
    Loop until a group is found that satisfies all query conditions or
    there are no satisfying groups left
  */
  do
  {
    result= next_prefix();
    if (result != 0)
      break;
    /*
      At this point this->record contains the current prefix in record format.
    */
    if (have_first)
    {
      first_res= next_min_max(!reverse, reverse);
      if (first_res == 0)
      {
        if (reverse)
          update_max_result();
        else
          update_min_result();
      }
    }
    /* If there is no FIRST in the group, there is no LAST either. */
    if ((have_last && !have_first) ||
        (have_last && have_first && (first_res == 0)))
    {
      last_res= next_min_max(reverse, reverse);
      if (last_res == 0)
      {
        if (reverse)
          update_min_result();
        else
          update_max_result();
      }
      /* If a LAST was found, a FIRST must have been found as well. */
      DBUG_ASSERT((have_last && !have_first) ||
                  (have_last && have_first && (last_res == 0)));
    }
    /*
      If this is just a GROUP BY or DISTINCT without MIN or MAX and there
      are equality predicates for the key parts after the group, find the
      first sub-group with the extended prefix.
    */
    if (!have_min && !have_max && key_infix_len > 0)
      result= file->ha_index_read_map(record, group_prefix,
                                      make_prev_keypart_map(real_key_parts),
                                      HA_READ_KEY_EXACT);

    result= have_first ? first_res : have_last ? last_res : result;
  } while (result == HA_ERR_KEY_NOT_FOUND || result == HA_ERR_END_OF_FILE);

  if (result == HA_ERR_KEY_NOT_FOUND)
    result= HA_ERR_END_OF_FILE;

  DBUG_RETURN(result);
}


/* Skip NULLs when looking for MIN. */

int QUICK_GROUP_MIN_MAX_SELECT::skip_nulls(bool reverse)
{
  int result= 0;
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::skip_nulls");
  /*
    If the min/max argument field is NULL, skip subsequent rows in the same
    group with NULL in it. Notice that:
    - if the first (or last with DESC index) row in a group doesn't have
      a NULL in the field, no row in the same group has (because NULL <
      any other value),
    - min_max_arg_part->field->ptr points to some place in 'record'.
  */
  DBUG_ASSERT(min_max_arg_part);
  if (min_max_arg_part->field->is_null())
  {
    uchar *tmp_key_buff= (uchar*)my_alloca(max_used_key_length);
    /* Find the first subsequent record without NULL in the MIN/MAX field. */
    key_copy(tmp_key_buff, record, index_info, max_used_key_length);
    result= file->ha_index_read_map(record, tmp_key_buff,
                                    make_keypart_map(real_key_parts),
                                    reverse ? HA_READ_BEFORE_KEY :
                                    HA_READ_AFTER_KEY);
    /*
      Check if the new record belongs to the current group by comparing its
      prefix with the group's prefix. If it is from the next group, then the
      whole group has NULLs in the MIN/MAX field, so use the first record in
      the group as a result.
      TODO:
      It is possible to reuse this new record as the result candidate for the
      next call to next_min_max(true, false), and to save one lookup in the
      next call. For this add a new member 'this->next_group_prefix'.
    */
    if (!result)
    {
      if (key_cmp(index_info->key_part, group_prefix, real_prefix_len))
        key_restore(record, tmp_key_buff, index_info, 0);
    }
    else if (result == HA_ERR_KEY_NOT_FOUND || result == HA_ERR_END_OF_FILE)
      result= 0; /* There is a result in any case. */
    my_afree(tmp_key_buff);
  }
  DBUG_RETURN(result);
}


/*
  Retrieve the min or max key in the next group.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::next_min_max()
    min                    [in] Whether retrieving min (true) or max (false)
    reverse                [in] Whether the key is a descending one

  DESCRIPTION
    Find the first key within this group such that the key satisfies the query
    conditions and NULL semantics. The found key is loaded into this->record.

  IMPLEMENTATION
    Depending on the values of min_max_ranges.elements, key_infix_len, and
    whether there is a NULL in the MIN field, this function may directly
    return without any data access. In this case we use the key loaded into
    this->record by the call to this->next_prefix() just before this call.

  RETURN
    0                    on success
    HA_ERR_KEY_NOT_FOUND if no min/max key was found that fulfills all
                         conditions.
    HA_ERR_END_OF_FILE   - "" -
    other                if some error occurred
*/

int QUICK_GROUP_MIN_MAX_SELECT::next_min_max(bool min, bool reverse)
{
  int result= 0;
  bool last= (min == reverse);
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::next_min_max");

  /* Find the min/max key using the eventually extended group prefix. */
  if (min_max_ranges.elements > 0)
    result= next_min_max_in_range(min, reverse);
  else
  {
    DBUG_ASSERT(min_max_arg_part);
    /*
      If we are looking for min/max on a reverse key with no range
      conditions for the min/max arg or infix equality conditions and
      the current (i.e. max) value is already NULL, the whole group
      has NULLs only in the min/max field.
    */
    if (reverse && key_infix_len == 0 && min_max_arg_part->field->is_null())
      DBUG_RETURN(0);
    if (last)
    {
      if ((result=
             file->ha_index_read_map(record, group_prefix,
                                     make_prev_keypart_map(real_key_parts),
                                     HA_READ_PREFIX_LAST)))
        DBUG_RETURN(result);
    }
    /*
      Apply the constant equality conditions to the non-group select
      fields
    */
    else if (key_infix_len > 0)
    {
      if ((result=
             file->ha_index_read_map(record, group_prefix,
                                     make_prev_keypart_map(real_key_parts),
                                     HA_READ_KEY_EXACT)))
        DBUG_RETURN(result);
    }
    /* Skip nulls if looking for MIN. */
    if (min)
      result= skip_nulls(reverse);
  }

  DBUG_RETURN(result);
}


/** 
  Find the next different key value by skipping all the rows with the same key
  value.

  Implements a specialized loose index access method for queries 
  containing aggregate functions with distinct of the form:
    SELECT [SUM|COUNT|AVG](DISTINCT a,...) FROM t
  This method comes to replace the index scan + Unique class 
  (distinct selection) for loose index scan that visits all the rows of a 
  covering index instead of jumping in the beginning of each group.
  TODO: Placeholder function. To be replaced by a handler API call

  @param is_index_scan     hint to use index scan instead of random index read 
                           to find the next different value.
  @param file              table handler
  @param key_part          group key to compare
  @param record            row data
  @param group_prefix      current key prefix data
  @param group_prefix_len  length of the current key prefix data
  @param group_key_parts   number of the current key prefix columns
  @return status
    @retval  0  success
    @retval !0  failure
*/

static int index_next_different (bool is_index_scan, handler *file, 
                                KEY_PART_INFO *key_part, uchar * record, 
                                const uchar * group_prefix,
                                uint group_prefix_len, 
                                uint group_key_parts)
{
  if (is_index_scan)
  {
    int result= 0;

    while (!key_cmp (key_part, group_prefix, group_prefix_len))
    {
      result= file->ha_index_next(record);
      if (result)
        return(result);
    }
    return result;
  }
  else
    return file->ha_index_read_map(record, group_prefix,
                                make_prev_keypart_map(group_key_parts),
                                HA_READ_AFTER_KEY);
}


/*
  Determine the prefix of the next group.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::next_prefix()

  DESCRIPTION
    Determine the prefix of the next group that satisfies the query conditions.
    If there is a range condition referencing the group attributes, use a
    QUICK_RANGE_SELECT object to retrieve the *first* key that satisfies the
    condition. If there is a key infix of constants, append this infix
    immediately after the group attributes. The possibly extended prefix is
    stored in this->group_prefix. The first key of the found group is stored in
    this->record, on which relies this->next_min().

  RETURN
    0                    on success
    HA_ERR_KEY_NOT_FOUND if there is no key with the formed prefix
    HA_ERR_END_OF_FILE   if there are no more keys
    other                if some error occurred
*/
int QUICK_GROUP_MIN_MAX_SELECT::next_prefix()
{
  int result;
  DBUG_ENTER("QUICK_GROUP_MIN_MAX_SELECT::next_prefix");

  if (quick_prefix_select)
  {
    uchar *cur_prefix= seen_first_key ? group_prefix : NULL;
    if ((result= quick_prefix_select->get_next_prefix(group_prefix_len,
                                                      group_key_parts, 
                                                      cur_prefix)))
      DBUG_RETURN(result);
    seen_first_key= TRUE;
  }
  else
  {
    if (!seen_first_key)
    {
      result= file->ha_index_first(record);
      if (result)
        DBUG_RETURN(result);
      seen_first_key= TRUE;
    }
    else
    {
      /* Load the first key in this group into record. */
      result= index_next_different (is_index_scan, file, index_info->key_part,
                            record, group_prefix, group_prefix_len, 
                            group_key_parts);
      if (result)
        DBUG_RETURN(result);
    }
  }

  /* Save the prefix of this group for subsequent calls. */
  key_copy(group_prefix, record, index_info, group_prefix_len);
  /* Append key_infix to group_prefix. */
  if (key_infix_len > 0)
    memcpy(group_prefix + group_prefix_len,
           key_infix, key_infix_len);

  DBUG_RETURN(0);
}


/**
  Allocate a temporary buffer, populate the buffer using the group prefix key
  and the min/max field key, and compare the result to the current key pointed
  by index_info.
  
  @param key    - the min or max field key
  @param length - length of "key"
*/
int
QUICK_GROUP_MIN_MAX_SELECT::cmp_min_max_key(const uchar *key, uint16 length)
{
  /*
    Allocate a buffer.
    Note, we allocate one extra byte, because some of Field_xxx::cmp(),
    e.g. Field_newdate::cmp(), use uint3korr() which actually read four bytes
    and then bit-and the read value with 0xFFFFFF.
    See "MDEV-7920 main.group_min_max fails ... with valgrind" for details.
  */
  uchar *buffer= (uchar*) my_alloca(real_prefix_len + min_max_arg_len + 1);
  /* Concatenate the group prefix key and the min/max field key */
  memcpy(buffer, group_prefix, real_prefix_len);
  memcpy(buffer + real_prefix_len, key, length);
  /* Compare the key pointed by key_info to the created key */
  int cmp_res= key_cmp(index_info->key_part, buffer,
                       real_prefix_len + min_max_arg_len);
  my_afree(buffer);
  return cmp_res;
}


/*
  Find the min/max key in a group that satisfies some range conditions
  for the min/max argument field.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::next_min_max_in_range()
    min                    [in] Whether finding min (true) or max (false))
    reverse                [in] Whether the key is a descending one

  DESCRIPTION
    Given the sequence of ranges min_max_ranges, find the min (resp.
    max) key that is in the leftmost (resp. rightmost) possible
    range. If there is no such key, then the current group does not
    have a min/max key that satisfies the WHERE clause. If a key is
    found, its value is stored in this->record.

  RETURN
    0                    on success
    HA_ERR_KEY_NOT_FOUND if there is no key with the given prefix in any of
                         the ranges
    HA_ERR_END_OF_FILE   - "" -
    other                if some error
*/

int QUICK_GROUP_MIN_MAX_SELECT::next_min_max_in_range(bool min, bool reverse)
{
  ha_rkey_function find_flag;
  key_part_map keypart_map;
  QUICK_RANGE *cur_range;
  int result= HA_ERR_KEY_NOT_FOUND;
  /* Whether looking for a last key (true) or a first key (false). */
  bool last= (min == reverse);
  bool found_null_for_min= FALSE;

  DBUG_ASSERT(min_max_ranges.elements > 0);

  /*
    Start from the leftmost (resp. rightmost) range if looking for min
    (resp. max).
  */
  for (size_t range_idx= 0; range_idx < min_max_ranges.elements; range_idx++)
  {
    get_dynamic(&min_max_ranges, (uchar*)&cur_range,
                min ? range_idx : min_max_ranges.elements - range_idx - 1);

    /*
      If the key has already been "moved" by a successful call to
      ha_index_read_map, and the current value for the max (resp. min)
      argument comes before (resp. after) the range, there is no need
      to check this range.
    */
    if (!result &&
        ((!min &&
          !(cur_range->flag & NO_MIN_RANGE) &&
          (key_cmp(min_max_arg_part, (const uchar*) cur_range->min_key,
                   min_max_arg_len) == (last ? -1 : 1))) ||
         (min &&
          !(cur_range->flag & NO_MAX_RANGE) &&
          (key_cmp(min_max_arg_part, (const uchar*) cur_range->max_key,
                   min_max_arg_len) == (last ? -1 : 1)))))
      continue;

    /*
      If the current range has no corresponding bound (i.e. upper
      bound for max and vice versa) for the key, set an unconditional
      find_flag.
    */
    if ((!min && cur_range->flag & NO_MAX_RANGE) ||
        (min && cur_range->flag & NO_MIN_RANGE))
    {
      keypart_map= make_prev_keypart_map(real_key_parts);
      find_flag= (last ? HA_READ_PREFIX_LAST : HA_READ_KEY_EXACT);
    }
    else
    {
      /*
        Extend the search key with the corresponding boundary (upper
        boundary for max and lower boundary for min) for this range,
        then set the correct flag. For example, if looking for min
        with descending index (hence last == true), and the current
        range has an open lower boundary (NEAR_MIN), the find_flag is
        HA_READ_BEFORE_KEY.
      */
      memcpy(group_prefix + real_prefix_len,
             min ? cur_range->min_key : cur_range->max_key,
             min ? cur_range->min_length : cur_range->max_length);
      keypart_map= make_keypart_map(real_key_parts);
      find_flag= (cur_range->flag & (EQ_RANGE | NULL_RANGE)) ?
                 HA_READ_KEY_EXACT :
                 ((!min && cur_range->flag & NEAR_MAX) ||
                  (min && cur_range->flag & NEAR_MIN)) ?
                  (last ? HA_READ_BEFORE_KEY : HA_READ_AFTER_KEY) :
                  (last ? HA_READ_PREFIX_LAST_OR_PREV : HA_READ_KEY_OR_NEXT);
    }

    result= file->ha_index_read_map(record, group_prefix, keypart_map,
                                    find_flag);

    /*
      If no key was found within this boundary: if the current range
      is an equality or IS NULL, check the next range, otherwise there
      certainly are no keys in subsequent ranges.
    */
    if (result)
    {
      if ((result == HA_ERR_KEY_NOT_FOUND || result == HA_ERR_END_OF_FILE) &&
          (cur_range->flag & (EQ_RANGE | NULL_RANGE)))
        continue;

      break;
    }
    /* A key was found. */
    if (cur_range->flag & EQ_RANGE)
      return 0; /* No need to perform the checks below for equal keys. */

    /* Check if record belongs to the current group. */
    if (key_cmp(index_info->key_part, group_prefix, real_prefix_len))
    {
      result= HA_ERR_KEY_NOT_FOUND;
      continue; // Row not found
    }

    /* Save a successful IS NULL lookup in case of min. */
    if (min && cur_range->flag & NULL_RANGE)
    {
      memcpy(tmp_record, record, head->s->reclength);
      found_null_for_min= TRUE;
      continue;
    }

    /*
      Compare the found key with the opposite boundary of the range
      (i.e. the lower boundary for max and vice versa) if the said
      boundary exists.
    */
    if ((!min && !(cur_range->flag & NO_MIN_RANGE)) ||
        (min && !(cur_range->flag & NO_MAX_RANGE)))
    {
      int cmp_res= min ?
        cmp_min_max_key(cur_range->max_key, cur_range->max_length) :
        cmp_min_max_key(cur_range->min_key, cur_range->min_length);
      /*
        The key is outside of the range if:

        - the max key (resp. min key) is equal to the open lower
          boundary (resp. upper boundary), OR
        - the max key (resp. min key) is less than the (open or
          closed) lower boundary (resp. greater than the upper
          boundary)
      */
      if ((((!min && cur_range->flag & NEAR_MIN) ||
            (min && cur_range->flag & NEAR_MAX)) &&
           cmp_res == 0) ||
          (last && cmp_res < 0) || (!last && cmp_res > 0))
      {
        result= HA_ERR_KEY_NOT_FOUND;
        continue;
      }
    }
    /* If we get to this point, the current key qualifies. */
    return result;
  }
  /*
    If no keys have been found except a NULL was found previously for
    an IS NULL in case of MIN, use it.
  */
  if (found_null_for_min)
  {
    memcpy(record, tmp_record, head->s->reclength);
    result= 0;
  }
  return result;
}


/*
  Update all MIN function results with the newly found value.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::update_min_result()

  DESCRIPTION
    The method iterates through all MIN functions and updates the result value
    of each function by calling Item_sum::reset(), which in turn picks the new
    result value from this->head->record[0], previously updated by
    next_min(). The updated value is stored in a member variable of each of the
    Item_sum objects, depending on the value type.

  IMPLEMENTATION
    The update must be done separately for MIN and MAX, immediately after
    next_min() was called and before next_max() is called, because both MIN and
    MAX take their result value from the same buffer this->head->record[0]
    (i.e.  this->record).

  RETURN
    None
*/

void QUICK_GROUP_MIN_MAX_SELECT::update_min_result()
{
  Item_sum *min_func;

  min_functions_it->rewind();
  while ((min_func= (*min_functions_it)++))
    min_func->reset_and_add();
}


/*
  Update all MAX function results with the newly found value.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::update_max_result()

  DESCRIPTION
    The method iterates through all MAX functions and updates the result value
    of each function by calling Item_sum::reset(), which in turn picks the new
    result value from this->head->record[0], previously updated by
    next_max(). The updated value is stored in a member variable of each of the
    Item_sum objects, depending on the value type.

  IMPLEMENTATION
    The update must be done separately for MIN and MAX, immediately after
    next_max() was called, because both MIN and MAX take their result value
    from the same buffer this->head->record[0] (i.e.  this->record).

  RETURN
    None
*/

void QUICK_GROUP_MIN_MAX_SELECT::update_max_result()
{
  Item_sum *max_func;

  max_functions_it->rewind();
  while ((max_func= (*max_functions_it)++))
    max_func->reset_and_add();
}


/*
  Append comma-separated list of keys this quick select uses to key_names;
  append comma-separated list of corresponding used lengths to used_lengths.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::add_keys_and_lengths()
    key_names    [out] Names of used indexes
    used_lengths [out] Corresponding lengths of the index names

  DESCRIPTION
    This method is used by select_describe to extract the names of the
    indexes used by a quick select.

*/

void QUICK_GROUP_MIN_MAX_SELECT::add_keys_and_lengths(String *key_names,
                                                      String *used_lengths)
{
  bool first= TRUE;

  add_key_and_length(key_names, used_lengths, &first);
}


/* Check whether the number for equality ranges exceeds the set threshold */ 

bool eq_ranges_exceeds_limit(RANGE_SEQ_IF *seq, void *seq_init_param,
                             uint limit)
{
  KEY_MULTI_RANGE range;
  range_seq_t seq_it;
  uint count = 0;

  if (limit == 0)
  {
    /* 'Statistics instead of index dives' feature is turned off */
   return false;
  }
  seq_it= seq->init(seq_init_param, 0, 0);
  while (!seq->next(seq_it, &range))
  {
    if ((range.range_flag & EQ_RANGE) && !(range.range_flag & NULL_RANGE))
    {
      if (++count >= limit)
        return true;
    }
  }
  return false;
}

#ifndef DBUG_OFF

static void print_sel_tree(PARAM *param, SEL_TREE *tree, key_map *tree_map,
                           const char *msg)
{
  char buff[1024];
  DBUG_ENTER("print_sel_tree");

  String tmp(buff,sizeof(buff),&my_charset_bin);
  tmp.length(0);
  for (uint idx= 0; idx < param->keys; idx++)
  {
    if (tree_map->is_set(idx))
    {
      uint keynr= param->real_keynr[idx];
      if (tmp.length())
        tmp.append(',');
      tmp.append(&param->table->key_info[keynr].name);
    }
  }
  if (!tmp.length())
    tmp.append(STRING_WITH_LEN("(empty)"));

  DBUG_PRINT("info", ("SEL_TREE: %p (%s)  scans: %s", tree, msg,
                      tmp.c_ptr_safe()));

  DBUG_VOID_RETURN;
}


static void print_ror_scans_arr(TABLE *table, const char *msg,
                                struct st_ror_scan_info **start,
                                struct st_ror_scan_info **end)
{
  DBUG_ENTER("print_ror_scans_arr");

  char buff[1024];
  String tmp(buff,sizeof(buff),&my_charset_bin);
  tmp.length(0);
  for (;start != end; start++)
  {
    if (tmp.length())
      tmp.append(',');
    tmp.append(&table->key_info[(*start)->keynr].name);
  }
  if (!tmp.length())
    tmp.append(STRING_WITH_LEN("(empty)"));
  DBUG_PRINT("info", ("ROR key scans (%s): %s", msg, tmp.c_ptr()));
  DBUG_VOID_RETURN;
}

static String dbug_print_sel_arg_buf;

static void
print_sel_arg_key(Field *field, const uchar *key, String *out)
{
  TABLE *table= field->table;
  MY_BITMAP *old_sets[2];
  dbug_tmp_use_all_columns(table, old_sets, &table->read_set, &table->write_set);

  if (field->real_maybe_null())
  {
    if (*key)
    {
      out->append(STRING_WITH_LEN("NULL"));
      goto end;
    }
    key++;					// Skip null byte
  }

  field->set_key_image(key, field->pack_length());

  if (field->type() == MYSQL_TYPE_BIT)
    (void) field->val_int_as_str(out, 1);
  else
    field->val_str(out);

end:
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);
}


/*
  @brief
    Produce a string representation of an individual SEL_ARG and return pointer
    to it

  @detail
    Intended usage:

     (gdb) p dbug_print_sel_arg(ptr)
*/

const char *dbug_print_sel_arg(SEL_ARG *sel_arg)
{
  StringBuffer<64> buf;
  String &out= dbug_print_sel_arg_buf;
  LEX_CSTRING tmp;
  out.length(0);

  if (!sel_arg)
  {
    out.append(STRING_WITH_LEN("NULL"));
    goto end;
  }

  out.append(STRING_WITH_LEN("SEL_ARG("));

  const char *stype;
  switch(sel_arg->type) {
  case SEL_ARG::IMPOSSIBLE:
    stype="IMPOSSIBLE";
    break;
  case SEL_ARG::MAYBE:
    stype="MAYBE";
    break;
  case SEL_ARG::MAYBE_KEY:
    stype="MAYBE_KEY";
    break;
  case SEL_ARG::KEY_RANGE:
  default:
    stype= NULL;
  }

  if (stype)
  {
    out.append(STRING_WITH_LEN("type="));
    out.append(stype, strlen(stype));
    goto end;
  }

  if (sel_arg->min_flag & NO_MIN_RANGE)
    out.append(STRING_WITH_LEN("-inf"));
  else
  {
    print_sel_arg_key(sel_arg->field, sel_arg->min_value, &buf);
    out.append(buf);
  }

  if (sel_arg->min_flag & NEAR_MIN)
    tmp = { STRING_WITH_LEN("<") };
  else
    tmp = { STRING_WITH_LEN("<=") };
  out.append(&tmp);

  out.append(sel_arg->field->field_name);

  if (sel_arg->min_flag & NEAR_MAX)
    tmp = { STRING_WITH_LEN("<") };
  else
    tmp = { STRING_WITH_LEN("<=") };
  out.append(&tmp);

  if (sel_arg->max_flag & NO_MAX_RANGE)
    out.append(STRING_WITH_LEN("+inf"));
  else
  {
    buf.length(0);
    print_sel_arg_key(sel_arg->field, sel_arg->max_value, &buf);
    out.append(buf);
  }

  out.append(')');

end:
  return dbug_print_sel_arg_buf.c_ptr_safe();
}


/*****************************************************************************
** Print a quick range for debugging
** TODO:
** This should be changed to use a String to store each row instead
** of locking the DEBUG stream !
*****************************************************************************/

static void
print_key(KEY_PART *key_part, const uchar *key, uint used_length)
{
  char buff[1024];
  const uchar *key_end= key+used_length;
  uint store_length;
  TABLE *table= key_part->field->table;
  MY_BITMAP *old_sets[2];

  dbug_tmp_use_all_columns(table, old_sets, &table->read_set, &table->write_set);

  for (; key < key_end; key+=store_length, key_part++)
  {
    String tmp(buff,sizeof(buff),&my_charset_bin);
    Field *field=      key_part->field;
    store_length= key_part->store_length;

    if (field->real_maybe_null())
    {
      if (*key)
      {
	fwrite("NULL",sizeof(char),4,DBUG_FILE);
	continue;
      }
      key++;					// Skip null byte
      store_length--;
    }
    field->set_key_image(key, key_part->length);
    if (field->type() == MYSQL_TYPE_BIT)
      (void) field->val_int_as_str(&tmp, 1);
    else
      field->val_str(&tmp);
    fwrite(tmp.ptr(),sizeof(char),tmp.length(),DBUG_FILE);
    if (key+store_length < key_end)
      fputc('/',DBUG_FILE);
  }
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);
}


static void print_quick(QUICK_SELECT_I *quick, const key_map *needed_reg)
{
  char buf[MAX_KEY/8+1];
  TABLE *table;
  MY_BITMAP *old_sets[2];
  DBUG_ENTER("print_quick");
  if (!quick)
    DBUG_VOID_RETURN;
  DBUG_LOCK_FILE;

  table= quick->head;
  dbug_tmp_use_all_columns(table, old_sets, &table->read_set, &table->write_set);
  quick->dbug_dump(0, TRUE);
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);

  fprintf(DBUG_FILE,"other_keys: 0x%s:\n", needed_reg->print(buf));

  DBUG_UNLOCK_FILE;
  DBUG_VOID_RETURN;
}

void QUICK_RANGE_SELECT::dbug_dump(int indent, bool verbose)
{
  /* purecov: begin inspected */
  fprintf(DBUG_FILE, "%*squick range select, key %s, length: %d\n",
	  indent, "", head->key_info[index].name.str, max_used_key_length);

  if (verbose)
  {
    QUICK_RANGE *range;
    QUICK_RANGE **pr= (QUICK_RANGE**)ranges.buffer;
    QUICK_RANGE **end_range= pr + ranges.elements;
    for (; pr != end_range; ++pr)
    {
      fprintf(DBUG_FILE, "%*s", indent + 2, "");
      range= *pr;
      if (!(range->flag & NO_MIN_RANGE))
      {
        print_key(key_parts, range->min_key, range->min_length);
        if (range->flag & NEAR_MIN)
	  fputs(" < ",DBUG_FILE);
        else
	  fputs(" <= ",DBUG_FILE);
      }
      fputs("X",DBUG_FILE);

      if (!(range->flag & NO_MAX_RANGE))
      {
        if (range->flag & NEAR_MAX)
	  fputs(" < ",DBUG_FILE);
        else
	  fputs(" <= ",DBUG_FILE);
        print_key(key_parts, range->max_key, range->max_length);
      }
      fputs("\n",DBUG_FILE);
    }
  }
  /* purecov: end */    
}

void QUICK_INDEX_SORT_SELECT::dbug_dump(int indent, bool verbose)
{
  List_iterator_fast<QUICK_RANGE_SELECT> it(quick_selects);
  QUICK_RANGE_SELECT *quick;
  fprintf(DBUG_FILE, "%*squick index_merge select\n", indent, "");
  fprintf(DBUG_FILE, "%*smerged scans {\n", indent, "");
  while ((quick= it++))
    quick->dbug_dump(indent+2, verbose);
  if (pk_quick_select)
  {
    fprintf(DBUG_FILE, "%*sclustered PK quick:\n", indent, "");
    pk_quick_select->dbug_dump(indent+2, verbose);
  }
  fprintf(DBUG_FILE, "%*s}\n", indent, "");
}

void QUICK_ROR_INTERSECT_SELECT::dbug_dump(int indent, bool verbose)
{
  List_iterator_fast<QUICK_SELECT_WITH_RECORD> it(quick_selects);
  QUICK_SELECT_WITH_RECORD *qr;
  fprintf(DBUG_FILE, "%*squick ROR-intersect select, %scovering\n",
          indent, "", need_to_fetch_row? "":"non-");
  fprintf(DBUG_FILE, "%*smerged scans {\n", indent, "");
  while ((qr= it++))
    qr->quick->dbug_dump(indent+2, verbose);
  if (cpk_quick)
  {
    fprintf(DBUG_FILE, "%*sclustered PK quick:\n", indent, "");
    cpk_quick->dbug_dump(indent+2, verbose);
  }
  fprintf(DBUG_FILE, "%*s}\n", indent, "");
}

void QUICK_ROR_UNION_SELECT::dbug_dump(int indent, bool verbose)
{
  List_iterator_fast<QUICK_SELECT_I> it(quick_selects);
  QUICK_SELECT_I *quick;
  fprintf(DBUG_FILE, "%*squick ROR-union select\n", indent, "");
  fprintf(DBUG_FILE, "%*smerged scans {\n", indent, "");
  while ((quick= it++))
    quick->dbug_dump(indent+2, verbose);
  fprintf(DBUG_FILE, "%*s}\n", indent, "");
}


/*
  Print quick select information to DBUG_FILE.

  SYNOPSIS
    QUICK_GROUP_MIN_MAX_SELECT::dbug_dump()
    indent  Indentation offset
    verbose If TRUE show more detailed output.

  DESCRIPTION
    Print the contents of this quick select to DBUG_FILE. The method also
    calls dbug_dump() for the used quick select if any.

  IMPLEMENTATION
    Caller is responsible for locking DBUG_FILE before this call and unlocking
    it afterwards.

  RETURN
    None
*/

void QUICK_GROUP_MIN_MAX_SELECT::dbug_dump(int indent, bool verbose)
{
  fprintf(DBUG_FILE,
          "%*squick_group_min_max_select: index %s (%d), length: %d\n",
	  indent, "", index_info->name.str, index, max_used_key_length);
  if (key_infix_len > 0)
  {
    fprintf(DBUG_FILE, "%*susing key_infix with length %d:\n",
            indent, "", key_infix_len);
  }
  if (quick_prefix_select)
  {
    fprintf(DBUG_FILE, "%*susing quick_range_select:\n", indent, "");
    quick_prefix_select->dbug_dump(indent + 2, verbose);
  }
  if (min_max_ranges.elements > 0)
  {
    fprintf(DBUG_FILE, "%*susing %zu quick_ranges for MIN/MAX:\n",
            indent, "", min_max_ranges.elements);
  }
}

#endif /* !DBUG_OFF */


/*
  @brief Print the comparison operator for the min range
*/

static void print_min_range_operator(String *out, const ha_rkey_function flag)
{
    if (flag == HA_READ_AFTER_KEY)
      out->append(STRING_WITH_LEN(" < "));
    else if (flag == HA_READ_KEY_EXACT || flag == HA_READ_KEY_OR_NEXT)
      out->append(STRING_WITH_LEN(" <= "));
    else
      out->append(STRING_WITH_LEN(" ? "));
}


/*
  @brief Print the comparison operator for the max range
*/

static void print_max_range_operator(String *out, const ha_rkey_function flag)
{
  if (flag == HA_READ_BEFORE_KEY)
    out->append(STRING_WITH_LEN(" < "));
  else if (flag == HA_READ_AFTER_KEY)
    out->append(STRING_WITH_LEN(" <= "));
  else
    out->append(STRING_WITH_LEN(" ? "));
}


static
void print_range(String *out, const KEY_PART_INFO *key_part,
                 KEY_MULTI_RANGE *range, uint n_key_parts)
{
  Check_level_instant_set check_field(current_thd, CHECK_FIELD_IGNORE);
  uint flag= range->range_flag;
  String key_name;
  key_name.set_charset(system_charset_info);
  key_part_map keypart_map= range->start_key.keypart_map |
                            range->end_key.keypart_map;

  if (flag & GEOM_FLAG)
  {
    /*
      The flags of GEOM ranges do not work the same way as for other
      range types, so printing "col < some_geom" doesn't make sense.
      Just print the column name, not operator.
    */
    print_keyparts_name(out, key_part, n_key_parts, keypart_map);
    out->append(STRING_WITH_LEN(" "));
    print_key_value(out, key_part, range->start_key.key,
                    range->start_key.length);
    return;
  }

  if (range->start_key.length)
  {
    print_key_value(out, key_part, range->start_key.key,
                    range->start_key.length);
    print_min_range_operator(out, range->start_key.flag);
  }

  print_keyparts_name(out, key_part, n_key_parts, keypart_map);

  if (range->end_key.length)
  {
    print_max_range_operator(out, range->end_key.flag);
    print_key_value(out, key_part, range->end_key.key,
                    range->end_key.length);
  }
}


/*
  @brief Print range created for non-indexed columns

  @param
    out                   output string
    field                 field for which the range is printed
    range                 range for the field
*/

static
void print_range_for_non_indexed_field(String *out, Field *field,
                                       KEY_MULTI_RANGE *range)
{
  TABLE *table= field->table;
  MY_BITMAP *old_sets[2];
  dbug_tmp_use_all_columns(table, old_sets, &table->read_set, &table->write_set);

  if (range->start_key.length)
  {
    field->print_key_part_value(out, range->start_key.key, field->key_length());
    print_min_range_operator(out, range->start_key.flag);
  }

  out->append(field->field_name);

  if (range->end_key.length)
  {
    print_max_range_operator(out, range->end_key.flag);
    field->print_key_part_value(out, range->end_key.key, field->key_length());
  }
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);
}



/*

  Add ranges to the trace
  For ex:
    lets say we have an index a_b(a,b)
    query: select * from t1 where a=2 and b=4 ;
    so we create a range:
      (2,4) <= (a,b) <= (2,4)
    this is added to the trace
*/

static void trace_ranges(Json_writer_array *range_trace,
                         PARAM *param, uint idx,
                         SEL_ARG *keypart,
                         const KEY_PART_INFO *key_parts)
{
  SEL_ARG_RANGE_SEQ seq;
  KEY_MULTI_RANGE range;
  range_seq_t seq_it;
  uint flags= 0;
  RANGE_SEQ_IF seq_if = {NULL, sel_arg_range_seq_init,
                         sel_arg_range_seq_next, 0, 0};
  KEY *keyinfo= param->table->key_info + param->real_keynr[idx];
  uint n_key_parts= param->table->actual_n_key_parts(keyinfo);
  DBUG_ASSERT(range_trace->trace_started());
  seq.keyno= idx;
  seq.key_parts= param->key[idx];
  seq.real_keyno= param->real_keynr[idx];
  seq.param= param;
  seq.start= keypart;
  /*
    is_ror_scan is set to FALSE here, because we are only interested
    in iterating over all the ranges and printing them.
  */
  seq.is_ror_scan= FALSE;
  const KEY_PART_INFO *cur_key_part= key_parts + keypart->part;
  seq_it= seq_if.init((void *) &seq, 0, flags);

  while (!seq_if.next(seq_it, &range))
  {
    StringBuffer<128> range_info(system_charset_info);
    print_range(&range_info, cur_key_part, &range, n_key_parts);
    range_trace->add(range_info.c_ptr_safe(), range_info.length());
  }
}

/**
  Print a key to a string

  @param[out] out          String the key is appended to
  @param[in]  key_part     Index components description
  @param[in]  key          Key tuple
  @param[in]  used_length  length of the key tuple
*/

static void print_key_value(String *out, const KEY_PART_INFO *key_part,
                            const uchar* key, uint used_length)
{
  out->append(STRING_WITH_LEN("("));
  Field *field= key_part->field;
  StringBuffer<128> tmp(system_charset_info);
  TABLE *table= field->table;
  uint store_length;
  MY_BITMAP *old_sets[2];
  dbug_tmp_use_all_columns(table, old_sets, &table->read_set, &table->write_set);
  const uchar *key_end= key+used_length;

  for (; key < key_end; key+=store_length, key_part++)
  {
    field= key_part->field;
    store_length= key_part->store_length;

    field->print_key_part_value(out, key, key_part->length);

    if (key + store_length < key_end)
      out->append(STRING_WITH_LEN(","));
  }
  dbug_tmp_restore_column_maps(&table->read_set, &table->write_set, old_sets);
  out->append(STRING_WITH_LEN(")"));
}

/**
  Print key parts involved in a range
  @param[out] out          String the key is appended to
  @param[in]  key_part     Index components description
  @param[in]  n_keypart    Number of keyparts in index
  @param[in]  keypart_map  map for keyparts involved in the range
*/

void print_keyparts_name(String *out, const KEY_PART_INFO *key_part,
                         uint n_keypart, key_part_map keypart_map)
{
  uint i;
  out->append(STRING_WITH_LEN("("));
  bool first_keypart= TRUE;
  for (i=0; i < n_keypart; key_part++, i++)
  {
    if (keypart_map & (1 << i))
    {
      if (first_keypart)
        first_keypart= FALSE;
      else
        out->append(STRING_WITH_LEN(","));
      out->append(key_part->field->field_name);
      if (key_part->key_part_flag & HA_REVERSE_SORT)
        out->append(STRING_WITH_LEN(" DESC"));
    }
    else
      break;
  }
  out->append(STRING_WITH_LEN(")"));
}
