Vælg den seneste besked mellem to brugeres kommunikation i mysql

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)

Jeg anbefaler at bruge unikt sekvens-id i din tabel for at undgå ekstern GROUP BY .Hvis du har stigende unikt message_id (dvs. større message_id svarer til senere sendtime ), ville forespørgslen være meget enklere:

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)