One common problem that my sequence method can help to solve is how to display the most recent entry that a user has made in each thread that the user has contributed to:
SELECT * FROM posts WHERE usedid = $userid AND postid IN
(SELECT t1.postid, COUNT(t1.postid) AS sequence, t1.postid <= t2.postid AS flg
FROM posts t1 INNER [...]
Find user’s most recent post in each thread