First off, the query that I'm using is this:

PHP Code:

$query = "SELECT 
 threads.id, 
 threads.subject,
 threads.timestamp,
 categories.name, 
 started.id AS starterid,
 started.username AS starter, 
 lastreply.id AS lastreplyid,
 lastreply.username AS lastreply
 FROM `threads`
 LEFT JOIN `users` AS started ON started.id = threads.started 
 LEFT JOIN `users` AS lastreply ON lastreply.id = threads.last_reply 
 LEFT JOIN `categories` ON categories.id = threads.category
 LIMIT 0,30"; 


What that does is get all the needed information from 4 tables to show the threads on the index.php page.

Im assuming most/all of you know how a forum generally works; and what I'd like to do is order the threads by according to a linked value from another table.

Example:

+----+-------------------------+---------+----------+------------+
| id | subject                 | started | category | timestamp  |
+----+-------------------------+---------+----------+------------+
|  1 | First Thread in Forum.  |       1 |        1 | 1184270342 |
|  2 | Second Thread in Forum. |       2 |        2 | 1184337553 |
|  3 | Third Thread in Forum.  |       1 |        2 | 1184690571 |
+----+-------------------------+---------+----------+------------+

Thats the threads table. and the posts are linked to the threads via the id. I'd like to take that and make a sql query much like this.

SELECT * FROM threads SORT BY posts.timestamp;

I know you cant do that, but thats as close as i can think.

If you already have the timestamp in the result-set, why don't you add the sort clause to the end of the join clause?

In the posts table you have id, thread_id, and timestamp. I wanted to order the threads by their corresponding rows in the posts table with the highest timestamp.

So that they'd automatically be sorted when someone posts a new reply.