Question

I’m building a basic forum, and i want to grab the list of threads created but also grab the most recent post from the post table so i can display last reply and time of last reply

How ever my attempt is causing duplicate results, i tried a LEFT JOIN and a INNER JOIN with the same outcome. I was hoping someone knew the solution.

This is my attempt:

SELECT  t1.username as thread_starter,
        t2.username as last_reply_username,
        t1.thread_time as thread_start,
        t2.post_time as last_reply_time,
        t1.title,
        t1.sticky 
FROM threads t1
     INNER JOIN posts t2
        ON t1.id = t2.threadid
ORDER BY t1.sticky DESC, t2.post_time DESC

Does any one know how i can solve the problem so it will only get the last and most recent post from the post table related to each thread without returning duplicate threads?

Answer 1

The idea behind the query below is that it finds the most recent post (post_time) from the post table for each threadid inside the subquery. Then it joins back on the original table post and threads table.

SELECT  a.username AS Thread_Starter,
        c.username AS Last_reply_username,
        a.thread_time AS Thread_Start,
        c.post_time AS Last_Reply_Time,
        a.Title,
        a.Sticky
FROM    threads a
        INNER JOIN
        (
            SELECT  threadID, MAX(Post_Time) lastPost
            FROM    post
            GROUP BY ThreadID
        ) b ON  a.threadID = b.threadID
        INNER JOIN post c
            ON  b.threadID = c.ThreadID AND
                b.lastPost = c.post_time
ORDER BY a.sticky DESC, c.post_time DESC