Whats wrong with this:

SELECT A.id_first, COUNT(DISTINCT b.id_msg) AD count, A.title, A.posted FROM threads!messages A LEFT OUTER JOIN threads!messages B ON A.id_msg = B.id_first WHERE A.id_msg <> 0 and a.id_prev = 0 and a.id_topic = ?liTopic GROUP BY A.id_first order by 4 desc