SELECT * FROM (SELECT `messages`.`uid_from`,`messages`.`uid_to`,`messages`.`id` as mid, `messages`.`message`,`users`.`user`, `users`.`id` as uid FROM `messages`
LEFT JOIN users ON users.id = uid_from
WHERE uid_to = '20' OR uid_from = '20'  AND users.id !='20' ORDER BY mid ASC )a
GROUP by uid