sql error

[manola]

Hi!

$querya = $vbulletin->db->query_read("
		SELECT post.postid, post.pagetext, post.userid, post.username, thread.forumid, thread.title as titulo, thread.threadid, forum.forumid, forum.title
		FROM " . TABLE_PREFIX . "post as post
		LEFT JOIN " . TABLE_PREFIX . "thread as thread on (post.threadid = thread.threadid)
		LEFT JOIN " . TABLE_PREFIX . "forum as forum on (thread.forumid = forum.forumid)
		WHERE forum.forumid not in ($excluded)
		ORDER BY postid DESC
		LIMIT $limit"
	);

I got this table
POST 4 - THREAD 1 - USERX
POST 3 - THREAD 2 - USERX
POST 2 - THREAD 1 - USERX
POST 1 - THREAD 3 - USERX

I only want 1 post from every thread, in this example last 4 posts, 2 from thread 1 and other 2 from thread 2 and 3. If I only want to show 1 post from thread 1.. What i have to make?

Thanks!