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MDEV-35592 Duplicate entry 'NULL' for key 'key0' with subquery cache

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Expression cache lookup is null rejecting, so parameters with NULL
never hit and were inserted into the cache table again and again.
After conversion of the cache to an on-disk table (where NULLs are
equal) such a repeated insert failed with ER_DUP_ENTRY.

Do not store rows which can not be looked up.

On 11.4 the cache is just switched off when the HEAP table is full,
so the test fails only after MDEV-9101 (11.5+, ES 11.4 via MENT-2067).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Oleksandr Byelkin
2026-10-15 10:15:40 +02:00
parent d0164223c5
commit 5c61f8e825
3 changed files with 55 additions and 0 deletions
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20
mysql-test/main/subselect_cache.result
View File

@@ -3960,5 +3960,25 @@ Note 1981 Aggregate function 'bit_or()' of SELECT #4 belongs to SELECT #3
Note 1276 Field or reference 'd' of SELECT #3 was resolved in SELECT #1
Note 1003 /* select#1 */ select `test`.`t1`.`c` AS `d` from `test`.`t1` join `test`.`t1` where <expr_cache><`test`.`t1`.`c`>((/* select#3 */ select ord(<expr_cache><`test`.`t1`.`c`,bit_or(`test`.`t1`.`c`),bit_or(`test`.`t1`.`c`)>((/* select#4 */ select bit_or(`test`.`t1`.`c`)))) from `test`.`t1` group by `test`.`t1`.`c`))
DROP TABLE t0, t1;
#
# MDEV-35592 ERROR 1062 (23000): Duplicate entry 'NULL' for key 'key0'
# on CONCAT in sub-query
#
CREATE TABLE t1 (a INT);
INSERT INTO t1
WITH RECURSIVE s(n) AS (SELECT 0 UNION ALL SELECT n + 1 FROM s WHERE n < 999)
SELECT n FROM s, (VALUES (1), (2), (3), (4)) AS x ORDER BY n;
INSERT INTO t1 VALUES (NULL), (NULL);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (1), (2);
SET @save_tmp_table_size= @@tmp_table_size;
SET @save_max_heap_table_size= @@max_heap_table_size;
SET tmp_table_size= 16384, max_heap_table_size= 16384;
SELECT COUNT(*) FROM t1 WHERE (SELECT b FROM t2 WHERE t2.b = t1.a) IS NULL;
COUNT(*)
3994
SET tmp_table_size= @save_tmp_table_size;
SET max_heap_table_size= @save_max_heap_table_size;
DROP TABLE t1, t2;
# End of 11.4 tests
SET optimizer_switch=@save_optimizer_switch;

23
mysql-test/main/subselect_cache.test
View File

@@ -1769,6 +1769,29 @@ EXPLAIN EXTENDED SELECT t2.d FROM (SELECT c AS d FROM t1) AS t2 JOIN t1 ON (
DROP TABLE t0, t1;
--echo #
--echo # MDEV-35592 ERROR 1062 (23000): Duplicate entry 'NULL' for key 'key0'
--echo # on CONCAT in sub-query
--echo #
CREATE TABLE t1 (a INT);
INSERT INTO t1
WITH RECURSIVE s(n) AS (SELECT 0 UNION ALL SELECT n + 1 FROM s WHERE n < 999)
SELECT n FROM s, (VALUES (1), (2), (3), (4)) AS x ORDER BY n;
INSERT INTO t1 VALUES (NULL), (NULL);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (1), (2);
SET @save_tmp_table_size= @@tmp_table_size;
SET @save_max_heap_table_size= @@max_heap_table_size;
SET tmp_table_size= 16384, max_heap_table_size= 16384;
SELECT COUNT(*) FROM t1 WHERE (SELECT b FROM t2 WHERE t2.b = t1.a) IS NULL;
SET tmp_table_size= @save_tmp_table_size;
SET max_heap_table_size= @save_max_heap_table_size;
DROP TABLE t1, t2;
--echo # End of 11.4 tests
SET optimizer_switch=@save_optimizer_switch;

12
sql/sql_expression_cache.cc
View File

@@ -271,6 +271,18 @@ my_bool Expression_cache_tmptable::put_value(Item *value)
DBUG_RETURN(FALSE);
}
/*
check_value() could not build the lookup key (e.g. NULL in the null
rejecting key part), so such a row would never be found. Do not store
it: duplicates of it are rejected after conversion to an on-disk table,
where NULLs are equal.
*/
if (ref.key_err)
{
DBUG_PRINT("info", ("Key can not be looked up, do not store it"));
DBUG_RETURN(FALSE);
}
*(items.head_ref())= value;
fill_record(table_thd, cache_table, cache_table->field, items, true, true,
true);