SELECT p.author_id member_id,
         m.name member_name,
         COUNT(p.pid) posts
    FROM forum_posts p
         INNER JOIN forum_members m
                    ON p.author_id = m.member_id
         INNER JOIN forum_topics t
                    ON t.forum_id = 120
                       AND t.tid = p.topic_id
   WHERE p.author_id != 0
         AND p.new_topic = 0
GROUP BY p.author_id
ORDER BY posts DESC
   LIMIT 1