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MDEV-27510 Query returns wrong result when using split optimization

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This bug may affect the queries that uses a grouping derived table with
grouping list containing references to columns from different tables if
the optimizer decides to employ the split optimization for the derived
table. In some very specific cases it may affect queries with a grouping
derived table that refers only one base table.
This bug was caused by an improper fix for the bug MDEV-25128. The fix
tried to get rid of the equality conditions pushed into the where clause
of the grouping derived table T to which the split optimization had been
applied. The fix erroneously assumed that only those pushed equalities
that were used for ref access of the tables referenced by T were needed.
In fact the function remove_const() that figures out what columns from the
group list can be removed if the split optimization is applied can uses
other pushed equalities as well.
This patch actually provides a proper fix for MDEV-25128. Rather than
trying to remove invalid pushed equalities referencing the fields of SJM
tables with a look-up access the patch attempts not to push such equalities.

Approved by Oleksandr Byelkin <sanja@mariadb.com>
This commit is contained in:
Igor Babaev
2022-01-24 23:14:46 -08:00
parent da37bfd8d6
commit 0041265671
5 changed files with 635 additions and 29 deletions
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18
sql/sql_select.cc
View File

@ -9755,6 +9755,9 @@ bool JOIN::get_best_combination()
hash_join= FALSE;
fix_semijoin_strategies_for_picked_join_order(this);
if (inject_splitting_cond_for_all_tables_with_split_opt())
DBUG_RETURN(TRUE);
JOIN_TAB_RANGE *root_range;
if (!(root_range= new (thd->mem_root) JOIN_TAB_RANGE))
@ -21863,21 +21866,6 @@ make_cond_for_table_from_pred(THD *thd, Item *root_cond, Item *cond,
cond->marker=3; // Checked when read
return (COND*) 0;
}
/*
If cond is an equality injected for split optimization then
a. when retain_ref_cond == false : cond is removed unconditionally
(cond that supports ref access is removed by the preceding code)
b. when retain_ref_cond == true : cond is removed if it does not
support ref access
*/
if (left_item->type() == Item::FIELD_ITEM &&
is_eq_cond_injected_for_split_opt((Item_func_eq *) cond) &&
(!retain_ref_cond ||
!test_if_ref(root_cond, (Item_field*) left_item,right_item)))
{
cond->marker=3;
return (COND*) 0;
}
}
cond->marker=2;
cond->set_join_tab_idx(join_tab_idx_arg);