$r=q("SELECT p.resource_id, p.id, p.filename, p.mimetype, p.imgscale, p.description, p.created FROM photo p INNER JOIN
(SELECT resource_id, max(imgscale) imgscale FROM photo WHERE uid = %d AND album = '%s' AND imgscale <= 4 AND photo_usage IN ( %d, %d ) $sql_extra GROUP BY resource_id) ph
ON (p.resource_id = ph.resource_id AND p.imgscale = ph.imgscale)