Different results of query with 'derived_merge=on';

CREATE TABLE t1 (pk int, i1 int NOT NULL);

INSERT INTO t1 VALUES (1, 4),(2, 6);

CREATE TABLE t2 (i2 int NOT NULL, d2 DATE NOT NULL);

#INSERT IGNORE INTO t2 VALUES (4, NULL);

INSERT INTO t2 VALUES (4, '0000-00-00');  ##the same case, there NULL was truncated to '0000-00-00'

SELECT t1.i1 FROM t1 JOIN (t2 JOIN (SELECT t1.* FROM t1) AS a1 ON a1.i1 = t2.i2) ON a1.pk = t2.d2;

SET SESSION optimizer_switch = 'derived_merge=off';

SELECT t1.i1 FROM t1 JOIN (t2 JOIN (SELECT t1.* FROM t1) AS a1 ON a1.i1 = t2.i2) ON a1.pk = t2.d2;

drop table t1, t2;

MariaDB [test]> SELECT t1.i1 FROM t1 JOIN (t2 JOIN (SELECT t1.* FROM t1) AS a1 ON a1.i1 = t2.i2) ON a1.pk = t2.d2;

Empty set, 2 warnings (0.000 sec)

Warning (Code 1292): Incorrect datetime value: '1' for column 'pk' at row 2

Warning (Code 1292): Incorrect datetime value: '1' for column 'pk' at row 2

MariaDB [test]> SET SESSION optimizer_switch = 'derived_merge=off';

Query OK, 0 rows affected (0.000 sec)

MariaDB [test]> SELECT t1.i1 FROM t1 JOIN (t2 JOIN (SELECT t1.* FROM t1) AS a1 ON a1.i1 = t2.i2) ON a1.pk = t2.d2;

+----+

| i1 |

+----+

|  4 |

|  6 |

+----+

2 rows in set, 2 warnings (0.000 sec)

Warning (Code 1292): Incorrect datetime value: '1' for column 'pk' at row 3

Warning (Code 1292): Incorrect datetime value: '1' for column 'pk' at row 3