I cant seem to get this to work correctly.

I am writing a little search query for my script but i want it to check multiple columns not just one.

This is the code for the query

Code PHP:
$sql = "SELECT a.*, u.user_id, u.username, u.user_colour from ".CLASSIFIEDS_TABLE." a, ". USERS_TABLE ." u 
				WHERE a.ad_description OR a.ad_title OR u.username LIKE '%$search%' and u.user_id = a.ad_poster_id ORDER BY a.ad_date DESC";

Rite now it is only looking in the u.username column not the other

Any ideas on a fix for this?