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Fixed a typo/bug that could lead to wrong selectivity numbers for

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tables retrieved by range scans.

Added comments forgotten in the previous patch.
This commit is contained in:
Igor Babaev
2013-04-17 16:15:22 -07:00
parent 2e54ad03ad
commit ac8333e46d
3 changed files with 38 additions and 7 deletions
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37
sql/sql_select.cc
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@ -6905,6 +6905,18 @@ double JOIN::get_examined_rows()
}
/**
@brief
Get the selectivity of equalities between columns when joining a table
@param join The optimized join
@param idx The number of tables in the evaluated partual join
@param s The table to be joined for evaluation
@param rem_tables The bitmap of tables to be joined later
@param keyparts The number of key parts to used when joining s
@param ref_keyuse_steps Array of references to keyuses employed to join s
*/
static
double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
table_map rem_tables, uint keyparts,
@ -7015,6 +7027,19 @@ double table_multi_eq_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
return sel;
}
/**
@brief
Get the selectivity of conditions when joining a table
@param join The optimized join
@param s The table to be joined for evaluation
@param rem_tables The bitmap of tables to be joined later
@retval
selectivity of the conditions imposed on the rows of s
*/
static
double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
table_map rem_tables)
@ -7034,7 +7059,7 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
{
if (pos->key == 0 && table_records > 0)
{
sel*= table->quick_rows[s->quick->index]/table_records;
sel/= table->quick_rows[s->quick->index]/table_records;
}
}
else if (pos->key != 0)
@ -7085,6 +7110,11 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
} while (keyuse->table == table && keyuse->key == key);
}
/*
If the field f from the table is equal to a field from one the
earlier joined tables then the selectivity of the range conditions
over the field f must be discounted.
*/
for (Field **f_ptr=table->field ; (field= *f_ptr) ; f_ptr++)
{
if (!bitmap_is_set(read_set, field->field_index) ||
@ -12275,9 +12305,9 @@ static COND *build_equal_items_for_cond(THD *thd, COND *cond,
@endcode
Thus, applying equalities from the where condition we basically
can get more freedom in performing join operations.
Althogh we don't use this property now, it probably makes sense to use
Although we don't use this property now, it probably makes sense to use
it in the future.
@param thd Thread handler
@param thd Thread handler
@param cond condition to build the multiple equalities for
@param inherited path to all inherited multiple equality items
@param join_list list of join tables to which the condition
@ -12286,6 +12316,7 @@ static COND *build_equal_items_for_cond(THD *thd, COND *cond,
for on expressions
@param[out] cond_equal_ref pointer to the structure to place built
equalities in
@param link_equal_items equal fields are to be linked
@return
pointer to the transformed condition containing multiple equalities