mysql> explain select id, confession from Confessions.confessions left join Confessions.scores on id = confession_id where score > 0.5 order by rand() limit 1;+----+-------------+-------------+--------+---------------+---------+---------+----------------------------------+------+----------------------------------------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+-------------+--------+---------------+---------+---------+----------------------------------+------+----------------------------------------------+| 1 | SIMPLE | scores | ALL | PRIMARY | NULL | NULL | NULL | 64 | Using where; Using temporary; Using filesort || 1 | SIMPLE | confessions | eq_ref | PRIMARY | PRIMARY | 4 | Confessions.scores.confession_id | 1 | Using where |+----+-------------+-------------+--------+---------------+---------+---------+----------------------------------+------+----------------------------------------------+2 rows in set (0.00 sec)mysql> explain select c.id, c.confession from Confessions.confessions as c INNER JOIN Confessions.scores as s ON (c.id=s.confession_id) WHERE s.score > 0.5 order by rand() limit 1;+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------------------------------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------------------------------------+| 1 | SIMPLE | s | ALL | PRIMARY | NULL | NULL | NULL | 64 | Using where; Using temporary; Using filesort || 1 | SIMPLE | c | eq_ref | PRIMARY | PRIMARY | 4 | Confessions.s.confession_id | 1 | Using where |+----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------------------------------------+2 rows in set (0.00 sec)