Select the Latest Message Between the communication of two user in mysql

Question

I have a simple table maintaining messages between users. The table structure looks like

     sender    receiver   message   sendtime
      1          2              


        

Answer 1

SELECT data.* FROM 
(SELECT MAX(sendtime) AS sendtime 
         FROM data 
         WHERE 1 IN (sender,receiver)
         GROUP BY IF (1 = sender,receiver,sender)) AS latest
LEFT JOIN data ON latest.sendtime = data.sendtime AND 1 IN (data.sender, data.receiver)
GROUP BY IF (1 = data.sender,data.receiver,data.sender)

I recommend to use unique sequence id in your table to avoid external GROUP BY. If you have incrementing unique message_id (i.e. bigger message_id corresponds to later sendtime), the query would be much simpler:

SELECT data.* FROM 
(SELECT MAX(message_id) AS message_id 
         FROM data 
         WHERE 1 IN (sender,receiver)
         GROUP BY IF (1 = sender,receiver,sender)) AS latest
LEFT JOIN data USING(message_id)