DROP TABLE IF EXISTS t1,t2;
CREATE TABLE t1 (a INT, b CHAR(8), pk INT AUTO_INCREMENT PRIMARY KEY) ENGINE=xengine;
INSERT INTO t1 (a,b) VALUES (1,'a'),(2,'b'),(3,'c'),(4,'d'),(5,'e'),(10000,'foobar');
INSERT INTO t1 (a,b) SELECT a, b FROM t1;
CREATE TABLE t2 (c CHAR(8), d INT, pk INT AUTO_INCREMENT PRIMARY KEY) ENGINE=xengine;
INSERT INTO t2 (c,d) SELECT b, a FROM t1;
UPDATE IGNORE t1 SET b = 'upd1' WHERE b IS NOT NULL ORDER BY a LIMIT 1;
SELECT a,b FROM t1 ORDER BY pk;
a	b
1	upd1
2	b
3	c
4	d
5	e
10000	foobar
1	a
2	b
3	c
4	d
5	e
10000	foobar
UPDATE t1, t2 SET b = 'upd2a', c = 'upd2b' 
WHERE c < b OR a != ( SELECT 1 UNION SELECT 2 );
ERROR 21000: Subquery returns more than 1 row
UPDATE IGNORE t1, t2 SET b = 'upd2a', c = 'upd2b' 
WHERE c < b OR a != ( SELECT 1 UNION SELECT 2 );
Warnings:
Warning	1242	Subquery returns more than 1 row
SELECT a,b FROM t1 ORDER BY pk;
a	b
1	upd2a
2	upd2a
3	upd2a
4	upd2a
5	upd2a
10000	upd2a
1	a
2	upd2a
3	upd2a
4	upd2a
5	upd2a
10000	upd2a
SELECT c,d FROM t2 ORDER BY pk;
c	d
upd2b	1
upd2b	2
upd2b	3
upd2b	4
upd2b	5
upd2b	10000
upd2b	1
upd2b	2
upd2b	3
upd2b	4
upd2b	5
upd2b	10000
DROP TABLE t1, t2;