Can't get MySQL JOINs to work right

[thincom2000]

I don't think this has the same meaning as what I suggested in my first post, but here it is with LEFT JOINs and still not working (database error):

SELECT thread.*, post.*, IF(thread.pollid = poll.pollid, 'poll.*', '')
FROM " . TABLE_PREFIX . "thread AS thread
LEFT JOIN " . TABLE_PREFIX . "post AS post ON (post.postid = thread.firstpostid)
IF(thread.pollid = poll.pollid, 'LEFT JOIN " . TABLE_PREFIX . "poll AS poll ON (poll.pollid = thread.pollid)', '')
WHERE thread.forumid = " . $forumid . "