DROP TABLE IF EXISTS t1;CREATE TABLE t1 (c1 VARCHAR(255), c2 VARCHAR(255), c3 INT);INSERT INTO t1 VALUES (REPEAT('x', 255), REPEAT('y', 255), 1);INSERT INTO t1 VALUES (REPEAT('x', 255), REPEAT('y', 255), 2);INSERT INTO t1 VALUES (REPEAT('x', 255), REPEAT('y', 255), 3);SELECT COUNT(*) FROM t1;COUNT(*)3drop table if exists t1;create table t1 (a int, unique index indexa (a));insert into t1 values (-1), (-4), (-2), (NULL);select -10 IN (select a from t1 FORCE INDEX (indexa));-10 IN (select a from t1 FORCE INDEX (indexa))NULL