> explain select * from activity where parent_id in (1,2,3); +----+-------------+----------+-------+---------------+--------+---------+------+------+-----------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------+-------+---------------+--------+---------+------+------+-----------------------+ | 1 | SIMPLE | activity | range | parent | parent | 9 | NULL | 3 | Using index condition | +----+-------------+----------+-------+---------------+--------+---------+------+------+-----------------------+ 1 row in set (0.07 sec) > set eq_range_index_dive_limit=2; Query OK, 0 rows affected (0.07 sec) > explain select * from activity where parent_id in (1,2,3); +----+-------------+----------+-------+---------------+--------+---------+------+--------+-----------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------+-------+---------------+--------+---------+------+--------+-----------------------+ | 1 | SIMPLE | activity | range | parent | parent | 9 | NULL | 269697 | Using index condition | +----+-------------+----------+-------+---------------+--------+---------+------+--------+-----------------------+ 1 row in set (0.07 sec)