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

To me it feels simpler to use an own ID based on the sender and receiver. No JOIN and just one GROUP BY needed:

SELECT sender, receiver, message, MAX(time)
FROM (
  SELECT *,
    CASE WHEN sender < receiver 
              THEN CONCAT(sender,'&', receiver)
              ELSE CONCAT(receiver,'&', sender) END AS fromto
  FROM data) AS a
GROUP BY fromto