sql - 用于返回最后一条消息的 SQL 查询

Question

例子：

我希望你明白。我正在尝试使用此查询，但它仅返回用户 1 发送的查询。我还需要发送给他的查询。但没有重复相同的参与者。

Answer 1

SELECT idMsg(Max), idFrom, idTo
FROM Messages
WHERE idFrom = 1 OR idTo = 1
GROUP BY idFrom
ORDER BY visualized DESC

或者

SELECT top 1 idMsg, idFrom, idTo
FROM Messages
WHERE idFrom = 1 OR idTo = 1
ORDER BY DESC

Answer 2

尝试：

select case when idfrom < idto then idfrom else idto end userid1,
       case when idfrom > idto then idfrom else idto end userid2,
       max(id) id
from messages
where 1 in (idfrom, idto)
group by
       case when idfrom < idto then idfrom else idto end,
       case when idfrom > idto then idfrom else idto end

Answer 3

询问：

SELECT m1.idMsg, m1.idFrom, m1.idTo
FROM Messages m1
WHERE m1.dataMsg = (SELECT MAX(m2.dataMsg)
                    FROM Messages m2
                    WHERE m2.idFrom = m1.idFrom
                    AND m2.idTo = m1.idTo) 

Answer 4

我会尝试类似的东西

SELECT MAX(id), idto, idfrom
FROM messages
WHERE idto = 1 OR idfrom = 1
GROUP BY idto, idfrom

它可能比你需要的多一点，但它很好而且清晰。

Answer 5

尝试：

SELECT idMsg, idFrom, idTo
FROM Messages
WHERE idFrom = 1 OR idTo = 1
GROUP BY idFrom
ORDER BY visualized DESC