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MDEV-24925: Server crashes in Item_subselect::init_expr_cache_tracker

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(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
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50
mysql-test/r/subselect4.result
View File

@ -2722,3 +2722,53 @@ SELECT a FROM t1 WHERE (a, a) IN (SELECT 1, 2) AND a = (SELECT MIN(b) FROM t2);
a
DROP TABLE t1,t2;
# End of 10.2 tests
#
# MDEV-24925: Server crashes in Item_subselect::init_expr_cache_tracker
#
CREATE TABLE t1 (id INT PRIMARY KEY);
INSERT INTO t1 VALUES (1),(2);
SELECT
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY f
);
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY f
)
1
SELECT
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY 1
);
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY 1
)
1
DROP TABLE t1;

32
mysql-test/t/subselect4.test
View File

@ -2237,3 +2237,35 @@ SELECT a FROM t1 WHERE (a, a) IN (SELECT 1, 2) AND a = (SELECT MIN(b) FROM t2);
DROP TABLE t1,t2;
--echo # End of 10.2 tests
--echo #
--echo # MDEV-24925: Server crashes in Item_subselect::init_expr_cache_tracker
--echo #
CREATE TABLE t1 (id INT PRIMARY KEY);
INSERT INTO t1 VALUES (1),(2);
SELECT
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY f
);
SELECT
1 IN (
SELECT
(SELECT COUNT(id)
FROM t1
WHERE t1_outer.id <> id
) AS f
FROM
t1 AS t1_outer
GROUP BY 1
);
DROP TABLE t1;

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();