SELECT ma_forum.*, ma_forum_cat.*
FROM ma_forum, ma_forum_cat
JOIN ma_forum_comentarios ON ma_forum_comentarios.not_id = ma_forum.not_id
WHERE ma_forum.notcat_id=ma_forum_cat.notcat_id AND ma_forum.notcat_id='".$notcat_id."'
AND ma_forum.not_status='Ativo'
GROUP BY ma_forum.not_id
ORDER BY MAX(ma_forum_comentarios.comnot_data) DESC
'on句'の不明な列'ma_forum.not_id'