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Bug#48177 - SELECTs with NOT IN subqueries containing NULL

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values return too many records

WHERE clauses with "outer_value_list NOT IN subselect" were
handled incorrectly if the outer value list contained multiple 
items where at least one of these could be NULL. The first 
outer record with NULL value was handled correctly, but if a 
second record with NULL value existed, the optimizer would 
choose to reuse the result it got on the last execution of the 
subselect. This is incorrect if the outer value list has 
multiple items.
     
The fix is to make Item_in_optimizer::val_int (in 
item_cmpfunc.cc) reuse the result of the latest execution
for NULL values only if all values in the outer_value_list 
are NULL.


mysql-test/r/subselect3.result:
  Added test for BUG#48177
mysql-test/t/subselect3.test:
  Added test for BUG#48177
sql/item_cmpfunc.cc:
  Make Item_in_optimizer::val_int (in item_cmpfunc.cc) reuse the result of the latest execution for NULL values only if all values in the outer_value_list are NULL.
This commit is contained in:
Jorgen Loland 2009-11-03 13:48:59 +01:00
commit bec35067d3
3 changed files with 189 additions and 42 deletions
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96
sql/item_cmpfunc.cc
View file

@ -1585,61 +1585,73 @@ longlong Item_in_optimizer::val_int()
if (cache->null_value)
{
/*
We're evaluating
"<outer_value_list> [NOT] IN (SELECT <inner_value_list>...)"
where one or more of the outer values is NULL.
*/
if (((Item_in_subselect*)args[1])->is_top_level_item())
{
/*
We're evaluating "NULL IN (SELECT ...)". The result can be NULL or
FALSE, and we can return one instead of another. Just return NULL.
We're evaluating a top level item, e.g.
"<outer_value_list> IN (SELECT <inner_value_list>...)",
and in this case a NULL value in the outer_value_list means
that the result shall be NULL/FALSE (makes no difference for
top level items). The cached value is NULL, so just return
NULL.
*/
null_value= 1;
}
else
{
if (!((Item_in_subselect*)args[1])->is_correlated &&
result_for_null_param != UNKNOWN)
/*
We're evaluating an item where a NULL value in either the
outer or inner value list does not automatically mean that we
can return NULL/FALSE. An example of such a query is
"<outer_value_list> NOT IN (SELECT <inner_value_list>...)"
The result when there is at least one NULL value is: NULL if the
SELECT evaluated over the non-NULL values produces at least
one row, FALSE otherwise
*/
Item_in_subselect *item_subs=(Item_in_subselect*)args[1];
bool all_left_cols_null= true;
const uint ncols= cache->cols();
/*
Turn off the predicates that are based on column compares for
which the left part is currently NULL
*/
for (uint i= 0; i < ncols; i++)
{
/* Use cached value from previous execution */
null_value= result_for_null_param;
if (cache->element_index(i)->null_value)
item_subs->set_cond_guard_var(i, FALSE);
else
all_left_cols_null= false;
}
else
if (!((Item_in_subselect*)args[1])->is_correlated &&
all_left_cols_null && result_for_null_param != UNKNOWN)
{
/*
We're evaluating "NULL IN (SELECT ...)". The result is:
FALSE if SELECT produces an empty set, or
NULL otherwise.
We disable the predicates we've pushed down into subselect, run the
subselect and see if it has produced any rows.
/*
This is a non-correlated subquery, all values in the outer
value list are NULL, and we have already evaluated the
subquery for all NULL values: Return the same result we
did last time without evaluating the subquery.
*/
Item_in_subselect *item_subs=(Item_in_subselect*)args[1];
if (cache->cols() == 1)
{
item_subs->set_cond_guard_var(0, FALSE);
(void) args[1]->val_bool_result();
result_for_null_param= null_value= !item_subs->engine->no_rows();
item_subs->set_cond_guard_var(0, TRUE);
}
else
{
uint i;
uint ncols= cache->cols();
/*
Turn off the predicates that are based on column compares for
which the left part is currently NULL
*/
for (i= 0; i < ncols; i++)
{
if (cache->element_index(i)->null_value)
item_subs->set_cond_guard_var(i, FALSE);
}
(void) args[1]->val_bool_result();
result_for_null_param= null_value= !item_subs->engine->no_rows();
/* Turn all predicates back on */
for (i= 0; i < ncols; i++)
item_subs->set_cond_guard_var(i, TRUE);
}
null_value= result_for_null_param;
}
else
{
/* The subquery has to be evaluated */
(void) args[1]->val_bool_result();
null_value= !item_subs->engine->no_rows();
if (all_left_cols_null)
result_for_null_param= null_value;
}
/* Turn all predicates back on */
for (uint i= 0; i < ncols; i++)
item_subs->set_cond_guard_var(i, TRUE);
}
return 0;
}