MySQL ordering rows by

Question

I'm trying to pull data from my forum_topics and forum_replies tables to get the last reply date;

SELECT 
    (SELECT date FROM forum_replies WHERE topic=5 AND date < NOW()
    ORDER BY id DESC LIMIT 1) as lastreply, 
    ft.* FROM forum_topics ft
    ORDER by lastreply DESC LIMIT 5

It's getting the lastreply data in the recordset, but not using it to ORDER the rows of the recordset.

I can see why, but not sure how to fix it?

Answer 1

You should use correlated subquery:

SELECT 
    (SELECT r.date FROM forum_replies r WHERE ft.topic = r.topic
    ORDER BY r.id DESC LIMIT 1) as lastreply, 
    ft.* 
FROM forum_topics ft
ORDER by lastreply DESC LIMIT 5