opt_sum.cc

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/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

   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 02110-1301  USA */


#include "sql_priv.h"
#include "key.h"                                // key_cmp_if_same
#include "sql_select.h"

static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref, Field* field,
                                Item *cond, uint *range_fl,
                                uint *key_prefix_length);
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
                            Item *cond, uint range_fl, uint prefix_len);
static int maxmin_in_range(bool max_fl, Field* field, Item *cond);


/*
  Get exact count of rows in all tables

  SYNOPSIS
    get_exact_records()
    tables              List of tables

  NOTES
    When this is called, we know all table handlers supports HA_HAS_RECORDS
    or HA_STATS_RECORDS_IS_EXACT

  RETURN
    ULONGLONG_MAX       Error: Could not calculate number of rows
    #                   Multiplication of number of rows in all tables
*/

static ulonglong get_exact_record_count(TABLE_LIST *tables)
{
  ulonglong count= 1;
  for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
  {
    ha_rows tmp= tl->table->file->records();
    if (tmp == HA_POS_ERROR)
      return ULONGLONG_MAX;
    count*= tmp;
  }
  return count;
}


static int get_index_min_value(TABLE *table, TABLE_REF *ref,
                               Item_field *item_field, uint range_fl,
                               uint prefix_len)
{
  int error;
  
  if (!ref->key_length)
    error= table->file->ha_index_first(table->record[0]);
  else 
  {
    /*
      Use index to replace MIN/MAX functions with their values
      according to the following rules:

      1) Insert the minimum non-null values where the WHERE clause still
         matches, or
      2) a NULL value if there are only NULL values for key_part_k.
      3) Fail, producing a row of nulls

      Implementation: Read the smallest value using the search key. If
      the interval is open, read the next value after the search
      key. If read fails, and we're looking for a MIN() value for a
      nullable column, test if there is an exact match for the key.
    */
    if (!(range_fl & NEAR_MIN))
      /* 
         Closed interval: Either The MIN argument is non-nullable, or
         we have a >= predicate for the MIN argument.
      */
      error= table->file->ha_index_read_map(table->record[0],
                                           ref->key_buff,
                                           make_prev_keypart_map(ref->key_parts),
                                           HA_READ_KEY_OR_NEXT);
    else
    {
      /*
        Open interval: There are two cases:
        1) We have only MIN() and the argument column is nullable, or
        2) there is a > predicate on it, nullability is irrelevant.
        We need to scan the next bigger record first.
        Open interval is not used if the search key involves the last keypart,
        and it would not work.
      */
      DBUG_ASSERT(prefix_len < ref->key_length);
      error= table->file->ha_index_read_map(table->record[0],
                                            ref->key_buff,
                                            make_prev_keypart_map(ref->key_parts),
                                            HA_READ_AFTER_KEY);
      /* 
         If the found record is outside the group formed by the search
         prefix, or there is no such record at all, check if all
         records in that group have NULL in the MIN argument
         column. If that is the case return that NULL.

         Check if case 1 from above holds. If it does, we should read
         the skipped tuple.
      */
      if (item_field->field->real_maybe_null() &&
          ref->key_buff[prefix_len] == 1 &&
          /*
            Last keypart (i.e. the argument to MIN) is set to NULL by
            find_key_for_maxmin only if all other keyparts are bound
            to constants in a conjunction of equalities. Hence, we
            can detect this by checking only if the last keypart is
            NULL.
          */
          (error == HA_ERR_KEY_NOT_FOUND ||
           key_cmp_if_same(table, ref->key_buff, ref->key, prefix_len)))
      {
        DBUG_ASSERT(item_field->field->real_maybe_null());
        error= table->file->ha_index_read_map(table->record[0],
                                             ref->key_buff,
                                             make_prev_keypart_map(ref->key_parts),
                                             HA_READ_KEY_EXACT);
      }
    }
  }
  return error;
}


static int get_index_max_value(TABLE *table, TABLE_REF *ref, uint range_fl)
{
  return (ref->key_length ?
          table->file->ha_index_read_map(table->record[0], ref->key_buff,
                                        make_prev_keypart_map(ref->key_parts),
                                        range_fl & NEAR_MAX ?
                                        HA_READ_BEFORE_KEY : 
                                        HA_READ_PREFIX_LAST_OR_PREV) :
          table->file->ha_index_last(table->record[0]));
}



int opt_sum_query(THD *thd,
                  TABLE_LIST *tables, List<Item> &all_fields, Item *conds)
{
  List_iterator_fast<Item> it(all_fields);
  int const_result= 1;
  bool recalc_const_item= false;
  ulonglong count= 1;
  bool is_exact_count= TRUE, maybe_exact_count= TRUE;
  table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
  Item *item;
  int error;

  DBUG_ENTER("opt_sum_query");

  const table_map where_tables= conds ? conds->used_tables() : 0;
  /*
    opt_sum_query() happens at optimization. A subquery is optimized once but
    executed possibly multiple times.
    If the value of the set function depends on the join's emptiness (like
    MIN() does), and the join's emptiness depends on the outer row, we cannot
    mark the set function as constant:
   */
  if (where_tables & OUTER_REF_TABLE_BIT)
    DBUG_RETURN(0);

  /*
    Analyze outer join dependencies, and, if possible, compute the number
    of returned rows.
  */
  for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
  {
    if (tl->join_cond() || tl->outer_join_nest())
    /* Don't replace expression on a table that is part of an outer join */
    {
      outer_tables|= tl->table->map;

      /*
        We can't optimise LEFT JOIN in cases where the WHERE condition
        restricts the table that is used, like in:
          SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition
          WHERE t2.field IS NULL;
      */
      if (tl->table->map & where_tables)
        DBUG_RETURN(0);
    }
    else
      used_tables|= tl->table->map;

    /*
      If the storage manager of 'tl' gives exact row count as part of
      statistics (cheap), compute the total number of rows. If there are
      no outer table dependencies, this count may be used as the real count.
      Schema tables are filled after this function is invoked, so we can't
      get row count.
      Derived tables aren't filled yet, their number of rows are estimates.
    */
    bool table_filled= !(tl->schema_table || tl->uses_materialization());
    if ((tl->table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) &&
        table_filled)
    {
      error= tl->fetch_number_of_rows();
      if(error)
      {
        tl->table->file->print_error(error, MYF(ME_FATALERROR));
        DBUG_RETURN(error);
      }
      count*= tl->table->file->stats.records;
    }
    else
    {
      maybe_exact_count&= test(table_filled &&
                               (tl->table->file->ha_table_flags() &
                                HA_HAS_RECORDS));
      is_exact_count= FALSE;
      count= 1;                                 // ensure count != 0
    }
  }

  /*
    Iterate through all items in the SELECT clause and replace
    COUNT(), MIN() and MAX() with constants (if possible).
  */

  while ((item= it++))
  {
    if (item->type() == Item::SUM_FUNC_ITEM)
    {
      Item_sum *item_sum= (((Item_sum*) item));
      switch (item_sum->sum_func()) {
      case Item_sum::COUNT_FUNC:
        /*
          If the expr in COUNT(expr) can never be null we can change this
          to the number of rows in the tables if this number is exact and
          there are no outer joins.
        */
        if (!conds && !((Item_sum_count*) item)->get_arg(0)->maybe_null &&
            !outer_tables && maybe_exact_count)
        {
          if (!is_exact_count)
          {
            if ((count= get_exact_record_count(tables)) == ULONGLONG_MAX)
            {
              /* Error from handler in counting rows. Don't optimize count() */
              const_result= 0;
              continue;
            }
            is_exact_count= 1;                  // count is now exact
          }
        }
        /* For result count of full-text search: If
           1. it is a single table query,
           2. the WHERE condition is a single MATCH expresssion,
           3. the table engine can provide the row count from FTS result, and
           4. the expr in COUNT(expr) can not be NULL,
           we do the full-text search now, and replace with the actual count.

           Note: Item_func_match::init_search() will be called again
                 later in the optimization phase by init_fts_funcs(),
                 but search will still only be done once.
        */
        else if (tables->next_leaf == NULL &&                             // 1 
                 conds && conds->type() == Item::FUNC_ITEM && 
                 ((Item_func*)conds)->functype() == Item_func::FT_FUNC && // 2
                 (tables->table->file->ha_table_flags() &
                  HA_CAN_FULLTEXT_EXT) &&                                 // 3
                 !((Item_sum_count*) item)->get_arg(0)->maybe_null)       // 4
        {
          Item_func_match* fts_item= static_cast<Item_func_match*>(conds); 
          fts_item->init_search(true);
          if (thd->is_error())
            break;
          count= fts_item->get_count();
        }
        else
          const_result= 0;

        if (const_result == 1) {
          ((Item_sum_count*) item)->make_const((longlong) count);
          recalc_const_item= true;
        }
          
        break;
      case Item_sum::MIN_FUNC:
      case Item_sum::MAX_FUNC:
      {
        int is_max= test(item_sum->sum_func() == Item_sum::MAX_FUNC);
        /*
          If MIN/MAX(expr) is the first part of a key or if all previous
          parts of the key is found in the COND, then we can use
          indexes to find the key.
        */
        Item *expr=item_sum->get_arg(0);
        if (expr->real_item()->type() == Item::FIELD_ITEM)
        {
          uchar key_buff[MAX_KEY_LENGTH];
          TABLE_REF ref;
          uint range_fl, prefix_len;

          ref.key_buff= key_buff;
          Item_field *item_field= (Item_field*) (expr->real_item());
          TABLE *table= item_field->field->table;

          /* 
            Look for a partial key that can be used for optimization.
            If we succeed, ref.key_length will contain the length of
            this key, while prefix_len will contain the length of 
            the beginning of this key without field used in MIN/MAX(). 
            Type of range for the key part for this field will be
            returned in range_fl.
          */
          if (table->file->inited || (outer_tables & table->map) ||
              !find_key_for_maxmin(is_max, &ref, item_field->field, conds,
                                   &range_fl, &prefix_len))
          {
            const_result= 0;
            break;
          }
          if ((error= table->file->ha_index_init((uint) ref.key, 1)))
          {
            table->file->print_error(error, MYF(0));
            table->set_keyread(FALSE);
            DBUG_RETURN(error);
          }

          error= is_max ?
                 get_index_max_value(table, &ref, range_fl) :
                 get_index_min_value(table, &ref, item_field, range_fl,
                                     prefix_len);

          /* Verify that the read tuple indeed matches the search key */
          if (!error && reckey_in_range(is_max, &ref, item_field->field, 
                                        conds, range_fl, prefix_len))
            error= HA_ERR_KEY_NOT_FOUND;
          table->set_keyread(FALSE);
          table->file->ha_index_end();
          if (error)
          {
            if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
              DBUG_RETURN(HA_ERR_KEY_NOT_FOUND); // No rows matching WHERE
            /* HA_ERR_LOCK_DEADLOCK or some other error */
            table->file->print_error(error, MYF(0));
            DBUG_RETURN(error);
          }
          removed_tables|= table->map;
        }
        else if (!expr->const_item() || conds || !is_exact_count)
        {
          /*
            We get here if the aggregate function is not based on a field.
            Example: "SELECT MAX(1) FROM table ..."

            This constant optimization is not applicable if
            1. the expression is not constant, or
            2. it is unknown if the query returns any rows. MIN/MAX must return
               NULL if the query doesn't return any rows. We can't determine
               this if:
               - the query has a condition, because, in contrast to the
                 "MAX(field)" case above, the condition will not be evaluated
                 against an index for this case, or
               - the storage engine does not provide exact count, which means
                 that it doesn't know whether there are any rows.
          */
          const_result= 0;
          break;
        }
        item_sum->set_aggregator(item_sum->has_with_distinct() ? 
                                 Aggregator::DISTINCT_AGGREGATOR :
                                 Aggregator::SIMPLE_AGGREGATOR);
        /*
          If count == 0 (so is_exact_count == TRUE) and
          there're no outer joins, set to NULL,
          otherwise set to the constant value.
        */
        if (!count && !outer_tables)
        {
          item_sum->aggregator_clear();
          // Mark the aggregated value as based on no rows
          item->no_rows_in_result();
        }
        else
          item_sum->reset_and_add();
        item_sum->make_const();
        recalc_const_item= 1;
        break;
      }
      default:
        const_result= 0;
        break;
      }
    }
    else if (const_result)
    {
      if (recalc_const_item)
        item->update_used_tables();
      if (!item->const_item())
        const_result= 0;
    }
  }

  if (thd->is_error())
    DBUG_RETURN(thd->get_stmt_da()->sql_errno());

  /*
    If we have a where clause, we can only ignore searching in the
    tables if MIN/MAX optimisation replaced all used tables
    We do not use replaced values in case of:
    SELECT MIN(key) FROM table_1, empty_table
    removed_tables is != 0 if we have used MIN() or MAX().
  */
  if (removed_tables && used_tables != removed_tables)
    const_result= 0;                            // We didn't remove all tables
  DBUG_RETURN(const_result);
}


bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
{
  Item *item;
  *inv_order= 0;
  switch (func_item->argument_count()) {
  case 0:
    /* MULT_EQUAL_FUNC */
    {
      Item_equal *item_equal= (Item_equal *) func_item;
      Item_equal_iterator it(*item_equal);
      args[0]= it++;
      if (it++)
        return 0;
      if (!(args[1]= item_equal->get_const()))
        return 0;
    }
    break;
  case 1:
    /* field IS NULL */
    item= func_item->arguments()[0];
    if (item->type() != Item::FIELD_ITEM)
      return 0;
    args[0]= item;
    break;
  case 2:
    /* 'field op const' or 'const op field' */
    item= func_item->arguments()[0];
    if (item->type() == Item::FIELD_ITEM)
    {
      args[0]= item;
      item= func_item->arguments()[1];
      if (!item->const_item())
        return 0;
      args[1]= item;
    }
    else if (item->const_item())
    {
      args[1]= item;
      item= func_item->arguments()[1];
      if (item->type() != Item::FIELD_ITEM)
        return 0;
      args[0]= item;
      *inv_order= 1;
    }
    else
      return 0;
    break;
  case 3:
    /* field BETWEEN const AND const */
    item= func_item->arguments()[0];
    if (item->type() == Item::FIELD_ITEM)
    {
      args[0]= item;
      for (int i= 1 ; i <= 2; i++)
      {
        item= func_item->arguments()[i];
        if (!item->const_item())
          return 0;
        args[i]= item;
      }
    }
    else
      return 0;
  }
  return 1;
}


static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo, 
                          KEY_PART_INFO *field_part, Item *cond,
                          key_part_map *key_part_used, uint *range_fl,
                          uint *prefix_len)
{
  DBUG_ENTER("matching_cond");
  if (!cond)
    DBUG_RETURN(TRUE);
  Field *field= field_part->field;
  if (!(cond->used_tables() & field->table->map))
  {
    /* Condition doesn't restrict the used table */
    DBUG_RETURN(TRUE);
  }
  if (cond->type() == Item::COND_ITEM)
  {
    if (((Item_cond*) cond)->functype() == Item_func::COND_OR_FUNC)
      DBUG_RETURN(FALSE);

    /* AND */
    List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
    Item *item;
    while ((item= li++))
    {
      if (!matching_cond(max_fl, ref, keyinfo, field_part, item,
                         key_part_used, range_fl, prefix_len))
        DBUG_RETURN(FALSE);
    }
    DBUG_RETURN(TRUE);
  }

  if (cond->type() != Item::FUNC_ITEM)
    DBUG_RETURN(FALSE);                                 // Not operator, can't optimize

  bool eq_type= 0;                            // =, <=> or IS NULL
  bool is_null_safe_eq= FALSE;                // The operator is NULL safe, e.g. <=> 
  bool noeq_type= 0;                          // < or >  
  bool less_fl= 0;                            // < or <= 
  bool is_null= 0;                            // IS NULL
  bool between= 0;                            // BETWEEN ... AND ... 

  switch (((Item_func*) cond)->functype()) {
  case Item_func::ISNULL_FUNC:
    is_null= 1;     /* fall through */
  case Item_func::EQ_FUNC:
    eq_type= TRUE;
    break;
  case Item_func::EQUAL_FUNC:
    eq_type= is_null_safe_eq= TRUE;
    break;
  case Item_func::LT_FUNC:
    noeq_type= 1;   /* fall through */
  case Item_func::LE_FUNC:
    less_fl= 1;      
    break;
  case Item_func::GT_FUNC:
    noeq_type= 1;   /* fall through */
  case Item_func::GE_FUNC:
    break;
  case Item_func::BETWEEN:
    between= 1;

    // NOT BETWEEN is equivalent to OR and is therefore not a conjunction
    if (((Item_func_between*)cond)->negated)
      DBUG_RETURN(false);

    break;
  case Item_func::MULT_EQUAL_FUNC:
    eq_type= 1;
    break;
  default:
    DBUG_RETURN(FALSE);                                        // Can't optimize function
  }
  
  Item *args[3];
  bool inv;

  /* Test if this is a comparison of a field and constant */
  if (!simple_pred((Item_func*) cond, args, &inv))
    DBUG_RETURN(FALSE);

  if (!is_null_safe_eq && !is_null &&
      (args[1]->is_null() || (between && args[2]->is_null())))
    DBUG_RETURN(FALSE);

  if (inv && !eq_type)
    less_fl= 1-less_fl;                         // Convert '<' -> '>' (etc)

  /* Check if field is part of the tested partial key */
  uchar *key_ptr= ref->key_buff;
  KEY_PART_INFO *part;
  for (part= keyinfo->key_part; ; key_ptr+= part++->store_length)

  {
    if (part > field_part)
      DBUG_RETURN(FALSE);                     // Field is beyond the tested parts
    if (part->field->eq(((Item_field*) args[0])->field))
      break;                        // Found a part of the key for the field
  }

  bool is_field_part= part == field_part;
  if (!(is_field_part || eq_type))
    DBUG_RETURN(FALSE);

  key_part_map org_key_part_used= *key_part_used;
  if (eq_type || between || max_fl == less_fl)
  {
    uint length= (key_ptr-ref->key_buff)+part->store_length;
    if (ref->key_length < length)
    {
    /* Ultimately ref->key_length will contain the length of the search key */
      ref->key_length= length;      
      ref->key_parts= (part - keyinfo->key_part) + 1;
    }
    if (!*prefix_len && part+1 == field_part)       
      *prefix_len= length;
    if (is_field_part && eq_type)
      *prefix_len= ref->key_length;
  
    *key_part_used|= (key_part_map) 1 << (part - keyinfo->key_part);
  }

  if (org_key_part_used == *key_part_used &&
    /*
      The current search key is not being extended with a new key part.  This
      means that the a condition is added a key part for which there was a
      previous condition. We can only overwrite such key parts in some special
      cases, e.g. a > 2 AND a > 1 (here range_fl must be set to something). In
      all other cases the WHERE condition is always false anyway.
    */
      (eq_type || *range_fl == 0))
      DBUG_RETURN(FALSE);

  if (org_key_part_used != *key_part_used ||
      (is_field_part && 
       (between || eq_type || max_fl == less_fl) && !cond->val_int()))
  {
    /*
      It's the first predicate for this part or a predicate of the
      following form  that moves upper/lower bounds for max/min values:
      - field BETWEEN const AND const
      - field = const 
      - field {<|<=} const, when searching for MAX
      - field {>|>=} const, when searching for MIN
    */

    if (is_null || (is_null_safe_eq && args[1]->is_null()))
    {
      /*
        If we have a non-nullable index, we cannot use it,
        since set_null will be ignored, and we will compare uninitialized data.
      */
      if (!part->field->real_maybe_null())
        DBUG_RETURN(false);
      part->field->set_null();
      *key_ptr= (uchar) 1;
    }
    else
    {
      /* Update endpoints for MAX/MIN, see function comment. */
      Item *value= args[between && max_fl ? 2 : 1];
      value->save_in_field_no_warnings(part->field, true);
      if (part->null_bit) 
        *key_ptr++= (uchar) test(part->field->is_null());
      part->field->get_key_image(key_ptr, part->length, Field::itRAW);
    }
    if (is_field_part)
    {
      if (between || eq_type)
        *range_fl&= ~(NO_MAX_RANGE | NO_MIN_RANGE);
      else
      {
        *range_fl&= ~(max_fl ? NO_MAX_RANGE : NO_MIN_RANGE);
        if (noeq_type)
          *range_fl|=  (max_fl ? NEAR_MAX : NEAR_MIN);
        else
          *range_fl&= ~(max_fl ? NEAR_MAX : NEAR_MIN);
      }
    }
  }
  else if (eq_type)
  {
    if ((!is_null && !cond->val_int()) ||
        (is_null && !test(part->field->is_null())))
     DBUG_RETURN(FALSE);                       // Impossible test
  }
  else if (is_field_part)
    *range_fl&= ~(max_fl ? NO_MIN_RANGE : NO_MAX_RANGE);
  DBUG_RETURN(TRUE);  
}


static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
                                Field* field, Item *cond,
                                uint *range_fl, uint *prefix_len)
{
  if (!(field->flags & PART_KEY_FLAG))
    return false;                               // Not key field

  DBUG_ENTER("find_key_for_maxmin");

  TABLE *table= field->table;
  uint idx= 0;

  KEY *keyinfo,*keyinfo_end;
  for (keyinfo= table->key_info, keyinfo_end= keyinfo+table->s->keys ;
       keyinfo != keyinfo_end;
       keyinfo++,idx++)
  {
    KEY_PART_INFO *part,*part_end;
    key_part_map key_part_to_use= 0;
    /*
      Perform a check if index is not disabled by ALTER TABLE
      or IGNORE INDEX.
    */
    if (!table->keys_in_use_for_query.is_set(idx))
      continue;
    uint jdx= 0;
    *prefix_len= 0;
    for (part= keyinfo->key_part, part_end= part + actual_key_parts(keyinfo) ;
         part != part_end ;
         part++, jdx++, key_part_to_use= (key_part_to_use << 1) | 1)
    {
      if (!(table->file->index_flags(idx, jdx, 0) & HA_READ_ORDER))
        DBUG_RETURN(false);

      /* Check whether the index component is partial */
      Field *part_field= table->field[part->fieldnr-1];
      if ((part_field->flags & BLOB_FLAG) ||
          part->length < part_field->key_length())
        break;

      if (field->eq(part->field))
      {
        ref->key= idx;
        ref->key_length= 0;
        ref->key_parts= 0;
        key_part_map key_part_used= 0;
        *range_fl= NO_MIN_RANGE | NO_MAX_RANGE;
        if (matching_cond(max_fl, ref, keyinfo, part, cond,
                          &key_part_used, range_fl, prefix_len) &&
            !(key_part_to_use & ~key_part_used))
        {
          if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
          {
            /*
              The query is on this form:

              SELECT MIN(key_part_k) 
              FROM t1 
              WHERE key_part_1 = const and ... and key_part_k-1 = const

              If key_part_k is nullable, we want to find the first matching row
              where key_part_k is not null. The key buffer is now {const, ...,
              NULL}. This will be passed to the handler along with a flag
              indicating open interval. If a tuple is read that does not match
              these search criteria, an attempt will be made to read an exact
              match for the key buffer.
            */
            /* Set the first byte of key_part_k to 1, that means NULL */
            ref->key_buff[ref->key_length]= 1;
            ref->key_length+= part->store_length;
            ref->key_parts++;
            DBUG_ASSERT(ref->key_parts == jdx+1);
            *range_fl&= ~NO_MIN_RANGE;
            *range_fl|= NEAR_MIN; // Open interval
          }
          /*
            The following test is false when the key in the key tree is
            converted (for example to upper case)
          */
          if (field->part_of_key.is_set(idx))
            table->set_keyread(TRUE);
          DBUG_RETURN(true);
        }
      }
    }
  }
  DBUG_RETURN(false);
}


static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
                            Item *cond, uint range_fl, uint prefix_len)
{
  if (key_cmp_if_same(field->table, ref->key_buff, ref->key, prefix_len))
    return 1;
  if (!cond || (range_fl & (max_fl ? NO_MIN_RANGE : NO_MAX_RANGE)))
    return 0;
  return maxmin_in_range(max_fl, field, cond);
}


static int maxmin_in_range(bool max_fl, Field* field, Item *cond)
{
  /* If AND/OR condition */
  if (cond->type() == Item::COND_ITEM)
  {
    List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
    Item *item;
    while ((item= li++))
    {
      if (maxmin_in_range(max_fl, field, item))
        return 1;
    }
    return 0;
  }

  if (cond->used_tables() != field->table->map)
    return 0;
  bool less_fl= 0;
  switch (((Item_func*) cond)->functype()) {
  case Item_func::BETWEEN:
    return cond->val_int() == 0;                // Return 1 if WHERE is false
  case Item_func::LT_FUNC:
  case Item_func::LE_FUNC:
    less_fl= 1;
  case Item_func::GT_FUNC:
  case Item_func::GE_FUNC:
  {
    Item *item= ((Item_func*) cond)->arguments()[1];
    /* In case of 'const op item' we have to swap the operator */
    if (!item->const_item())
      less_fl= 1-less_fl;
    /*
      We only have to check the expression if we are using an expression like
      SELECT MAX(b) FROM t1 WHERE a=const AND b>const
      not for
      SELECT MAX(b) FROM t1 WHERE a=const AND b<const
    */
    if (max_fl != less_fl)
      return cond->val_int() == 0;                // Return 1 if WHERE is false
    return 0;
  }
  case Item_func::EQ_FUNC:
  case Item_func::EQUAL_FUNC:
    break;
  default:                                        // Keep compiler happy
    DBUG_ASSERT(1);                               // Impossible
    break;
  }
  return 0;
}