Private chat system MYSQL query to display last message of sender/receiver
message_id|sender_id||receiver_id|message_text|   created_time
    1         101          102       Message A    2012-06-07 08:07:18
    2         101          102       Message B    2012-06-07 08:10:20
    3         103          102       Message C    2012-06-07 08:12:43

id  | name
 101   bob
 102   jack
 103   mark

name|message_text |  created_time
      mark   message C    2012-06-07 08:12:43
      bob    message B    2012-06-07 08:10:20

SELECT * FROM messages,users
WHERE messages.receiver_id = 102
AND messages.sender_id=users.id
AND messages.created_time IN
(SELECT MAX(created_time)
FROM messages
GROUP BY sender_id)
ORDER BY messages.created_time DESC

name|message_text |  created_time
      mark   message D    2012-06-07 08:12:48
      bob    message B    2012-06-07 08:10:20

SELECT users.name,
       temp.MESSAGE_TEXT,
       temp.created_time
FROM
  (SELECT sender_id, MESSAGE_TEXT, created_time
   FROM messages
   WHERE created_time IN
       (SELECT MAX(created_time)
        FROM messages
        GROUP BY sender_id)) AS temp
LEFT JOIN users ON temp.sender_id = users.id;