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)
Doporučuji ve vaší tabulce použít jedinečné ID sekvence, abyste se vyhnuli externímu GROUP BY
.Pokud máte zvyšující se jedinečné message_id
(tj. větší message_id
odpovídá pozdějšímu sendtime
), dotaz by byl mnohem jednodušší:
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)