database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-29 05:21:33 +03:00
Code Activity

MDEV-24925: Server crashes in Item_subselect::init_expr_cache_tracker

Browse Source 
(trivial backport to 10.2)
The optimizer removes redundant GROUP BY operations. If GROUP BY element
is a subselect, it is "eliminated".

However one must not eliminate the item if it is used both in the select
list and in the GROUP BY, like so:

  select (select ... ) as SUBQ from ... group by SUBQ

Do not eliminate such items.
This commit is contained in:
Sergei Petrunia
2021-04-23 19:28:48 +03:00
parent 14a18d7d7f
commit c72c77ca3b
3 changed files with 92 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
sql/sql_select.cc
View File

@ -585,7 +585,16 @@ void remove_redundant_subquery_clauses(st_select_lex *subq_select_lex)
{
for (ORDER *ord= subq_select_lex->group_list.first; ord; ord= ord->next)
{
(*ord->item)->walk(&Item::eliminate_subselect_processor, FALSE, NULL);
/*
Do not remove the item if it is used in select list and then referred
from GROUP BY clause by its name or number. Example:
select (select ... ) as SUBQ ... group by SUBQ
Here SUBQ cannot be removed.
*/
if (!ord->in_field_list)
(*ord->item)->walk(&Item::eliminate_subselect_processor, FALSE, NULL);
}
subq_select_lex->join->group_list= NULL;
subq_select_lex->group_list.empty();