I+----+-------------+----------------+--------+-----------------------------------------------------+-------------------------+---------+-----------------------------------+-------+---------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+--------+-----------------------------------------------------+-------------------------+---------+-----------------------------------+-------+---------------------------------+ | 1 | PRIMARY | | ALL | NULL | NULL | NULL | NULL | 1810 | Using temporary; Using filesort | | 1 | PRIMARY | otheruser | range | PRIMARY,mdl_user_del_ix | mdl_user_del_ix | 1 | NULL | 5607 | Using where; Using join buffer | | 1 | PRIMARY | contact | ref | mdl_messcont_usecon_uix | mdl_messcont_usecon_uix | 8 | const | 3 | | | 1 | PRIMARY | message | eq_ref | PRIMARY,mdl_messread_use2_ix,mdl_messread_useuse_ix | PRIMARY | 8 | messagesubset.messageid | 1 | Using where | | 2 | DERIVED | | ALL | NULL | NULL | NULL | NULL | 1810 | Using temporary; Using filesort | | 2 | DERIVED | matchedmessage | ref | mdl_messread_use2_ix,mdl_messread_useuse_ix | mdl_messread_useuse_ix | 16 | recent.useridfrom,recent.useridto | 1 | Using where | | 3 | DERIVED | recentmessages | index | mdl_messread_use2_ix,mdl_messread_useuse_ix | mdl_messread_useuse_ix | 16 | NULL | 25175 | Using where | +----+-------------+----------------+--------+-----------------------------------------------------+-------------------------+---------+-----------------------------------+-------+---------------------------------+ 7 rows in set (0.05 sec)