Comment 2 for bug 813473

An example that demonstrates that the wrong result is
reproducible without constant tables:

CREATE TABLE t1 (c int) ;
INSERT INTO t1 VALUES (5),(6);

CREATE TABLE t2 (a int, b int) ;
INSERT INTO t2 VALUES (20,9),(20,9);

create table t3 (d int, e int);
insert into t3 values (2, 9), (3,10);

EXPLAIN
SELECT t2.b , t1.c
FROM t2 LEFT JOIN t1 ON t1.c < 3
WHERE ( t2.b , t1.c ) NOT IN ( SELECT * from t3);

SELECT t2.b , t1.c
FROM t2 LEFT JOIN t1 ON t1.c < 3
WHERE (t2.b, t1.c) NOT IN ( SELECT * from t3);