ELECT u.id, tmp.*
FROM USER u,
(  SELECT c.user1_id, COUNT(m.id)
   FROM conversation c
   JOIN message m ON m.conversation_id = c.id
   GROUP BY c.user1_id
) tmp
WHERE
 tmp.user1_id = u.id AND
 u.last_login_time >= 1452610663 - 3600;