php selecting an order from a different mysql table - php

Question

Hi I am trying to retrieve my topics from table topics but in my look up list I want the most recent active topic to be showing, all the comments are in different table. How could I do it that my list shows all the topics from the topics table but puts them in order according to the most recent date from the comments table?
$forums = mysql_query("select * from forumtopic where category='$who' order by date DESC LIMIT " . (($page - 1) * 10) . ", 10");
while($forum = mysql_fetch_array($forums))
{
so I want it to be like
$forums = mysql_query("select * from forumtopic where category='$who' and select from forumcomment where category='$who' but order by date from forumcomment DESC LIMIT " . (($page - 1) * 10) . ", 10");
while($forum = mysql_fetch_array($forums))
{
if that makes sense

Answer 1

I believe this is what you wanted to do:
SELECT * FROM forumtopic
WHERE category='$who'
ORDER BY FIELD( topic,
(SELECT topic
FROM forumcomment
WHERE category='$who'
ORDER BY date DESC))
LIMIT " . (($page - 1) * 10) . ", 10
The order by field lets you specify an order for the table forumtopic, which is ordered by most active, also I don't know the schema of your table so you have to change the names accordingly
EDIT - SIMPLER SOLUTION, JOIN THEN ORDER BY
SELECT forumtopic.topic FROM forumtopic
INNER JOIN forumcomment
ON forumtopic.topic = forumcomment.topic
WHERE category = '$who'
ORDER BY forumcomment.date DESC
LIMIT " . (($page - 1) * 10) . ", 10