MySQL obtém lista ordenada de contatos pela última mensagem enviada/recebida

SELECT messages.* FROM messages, (SELECT MAX(id) as lastid
                   FROM messages
                   WHERE (messages.receiver_id = '$myid' OR messages.sender_id = '$myid')

                   GROUP BY CONCAT(LEAST(messages.receiver_id,messages.sender_id),'.',
                   GREATEST(messages.receiver_id, messages.sender_id))) as conversations
                   WHERE id = conversations.lastid
                   ORDER BY messages.time DESC