Unknown column 'comment_id' in 'on clause'
SELECT count(cv2.vote_user) as votes, cv.vote_value as voted, comment_id, comment_user, comment_datetime, comment_text, comment_rating, u_login, u_avatar from comments, users LEFT JOIN comments_votes cv ON (cv.vote_comment=comment_id) LEFT JOIN comments_votes cv2 ON (cv2.vote_comment=comment_id) WHERE comment_item=12421 AND u_id=comment_user GROUP BY comment_id

Unknown column 'set_id' in 'on clause'
SELECT count(si2.si_item_id) as count, set_id, set_name, set_description, set_collection, set_public FROM sets, sets_items si LEFT JOIN sets_items si2 ON (set_id=si2.si_set_id) WHERE si.si_item_id=12421 AND si.si_set_id=set_id GROUP BY set_id