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Fixed bug #25407.

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The bug could cause choosing a sub-optimal execution plan for 
a single-table query if a unique index with many null keys were 
defined for the table. 
It happened because the code of the check_quick_keys function 
made an assumption that any key may occur in an unique index 
only once. Yet this is not true for keys with nulls that may 
have multiple occurrences in the index.
This commit is contained in:
igor@olga.mysql.com
2007-01-31 19:31:36 -08:00
parent 8760182170
commit 710136217b
4 changed files with 173 additions and 3 deletions
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12
sql/opt_range.cc
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@ -193,6 +193,8 @@ public:
}
inline void merge_flags(SEL_ARG *arg) { maybe_flag|=arg->maybe_flag; }
inline void maybe_smaller() { maybe_flag=1; }
/* Return true iff it's a single-point null interval */
inline bool is_null_interval() { return maybe_null && max_value[0] == 1; }
inline int cmp_min_to_min(SEL_ARG* arg)
{
return sel_cmp(field,min_value, arg->min_value, min_flag, arg->min_flag);
@ -452,6 +454,7 @@ typedef struct st_qsel_param {
bool is_ror_scan;
/* Number of ranges in the last checked tree->key */
uint n_ranges;
uint8 first_null_comp; /* first null component if any, 0 - otherwise */
} PARAM;
class TABLE_READ_PLAN;
@ -5619,6 +5622,7 @@ check_quick_select(PARAM *param,uint idx,SEL_ARG *tree)
DBUG_ENTER("check_quick_select");
param->is_ror_scan= FALSE;
param->first_null_comp= 0;
if (!tree)
DBUG_RETURN(HA_POS_ERROR); // Can't use it
@ -5710,6 +5714,7 @@ check_quick_keys(PARAM *param,uint idx,SEL_ARG *key_tree,
ha_rows records=0, tmp;
uint tmp_min_flag, tmp_max_flag, keynr, min_key_length, max_key_length;
char *tmp_min_key, *tmp_max_key;
uint8 save_first_null_comp= param->first_null_comp;
param->max_key_part=max(param->max_key_part,key_tree->part);
if (key_tree->left != &null_element)
@ -5747,6 +5752,9 @@ check_quick_keys(PARAM *param,uint idx,SEL_ARG *key_tree,
param->is_ror_scan= FALSE;
}
if (!param->first_null_comp && key_tree->is_null_interval())
param->first_null_comp= key_tree->part+1;
if (key_tree->next_key_part &&
key_tree->next_key_part->part == key_tree->part+1 &&
key_tree->next_key_part->type == SEL_ARG::KEY_RANGE)
@ -5790,7 +5798,8 @@ check_quick_keys(PARAM *param,uint idx,SEL_ARG *key_tree,
(param->table->key_info[keynr].flags & (HA_NOSAME | HA_END_SPACE_KEY)) ==
HA_NOSAME &&
min_key_length == max_key_length &&
!memcmp(param->min_key,param->max_key,min_key_length))
!memcmp(param->min_key,param->max_key,min_key_length) &&
!param->first_null_comp)
{
tmp=1; // Max one record
param->n_ranges++;
@ -5865,6 +5874,7 @@ check_quick_keys(PARAM *param,uint idx,SEL_ARG *key_tree,
return tmp;
records+=tmp;
}
param->first_null_comp= save_first_null_comp;
return records;
}