CREATE TABLE t1 (i INT AUTO_INCREMENT, c VARCHAR(1), KEY(i), KEY(c,i)) ENGINE=MyISAM; INSERT INTO t1 (c) select mid("abcdefgh", mod(seq,8)+1, 1) from seq_1_to_256; explain SELECT 1 FROM t1 AS alias1, t1 AS alias2, t1 AS alias3 WHERE alias1.c = alias2.c OR alias1.i <= 1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE alias2 index c c 8 NULL 256 Using index 1 SIMPLE alias3 index NULL i 4 NULL 256 Using index; Using join buffer (flat, BNL join) 1 SIMPLE alias1 ALL i,c NULL NULL NULL 256 Range checked for each record (index map: 0x3) set @old_dbug=@@session.debug_dbug; SET debug_dbug="+d,kill_join_init_read_record"; SELECT 1 FROM t1 AS alias1, t1 AS alias2, t1 AS alias3 WHERE alias1.c = alias2.c OR alias1.i <= 1 ; ERROR 70100: Query execution was interrupted SET debug_dbug=@old_dbug; DROP TABLE t1;