SELECT count(DISTINCT postkey) as post_count, membername FROM members, posts where members.memberid = posts.postauthorid GROUP BY membername ORDER BY post_count DESC
Posting that query is mostly for archival purposes. Basically this.. fun little query counts the number of unique posts by each user, from a MySQL database.
The posts table has postkey (the unique identifier) and postauthorid, the members table has a membersid column (relates to postauthorid) and membersname (the human-readable member's name).