2011-11-03 18:03:31.963407+00:00 https://api.launchpad.net/1.0/bugs/885799 https://api.launchpad.net/1.0/~sergefp https://api.launchpad.net/1.0/bugs/885799/linked_branches https://api.launchpad.net/1.0/bugs/885799/activity https://bugs.launchpad.net/bugs/885799 Sergey Petrunia New Undecided 2011-11-03 18:03:31.963407+00:00 3" is a cheap constant condition that evaluates to FALSE: MariaDB [j10]> explain select * from t_pk1, t2 where t_pk1.a=2 and t_pk1.b> 3 ; +----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE noticed after reading const tables | +----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+ 1 row in set (0.00 sec) # Now, let's add an expensive constant condition, and observe that we won't be getting "Impossible WHERE" anymore: MariaDB [j10]> explain select * from t_pk1, t2 where t_pk1.a=2 and t_pk1.b> 3 and 2 > (select max(a) from t1); +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+ | 1 | PRIMARY | t_pk1 | const | PRIMARY | PRIMARY | 4 | const | 1 | | | 1 | PRIMARY | t2 | ALL | NULL | NULL | NULL | NULL | 3 | | | 2 | SUBQUERY | t1 | ALL | NULL | NULL | NULL | NULL | 3 | | +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------+ 3 rows in set (0.00 sec)]]> bug Sergey Petrunia added bug