UPDATE: * s/Using join cache/Using join buffer/, changed to show the final variants of EXPLAIN output as described here * s/join_buff_size/join_buffer_size/ Starting from 5.1.18, EXPLAIN output may show “Using join cache“, like in this example: mysql> explain select * from t1, t2 where t1.col < 10 and t2.col < 'bar'; +----+-------------+-------+-------+-...-+--------------------------------+ | id