SQL查詢返回的最後一封郵件

Question

例子：

我希望你能理解。 我正在嘗試使用此查詢，但它只返回用戶1發送的那些查詢。我還需要那些發送給他的查詢。但沒有重複相同的參與者。

Answer 1

嘗試：

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

Answer 2

我會嘗試像

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

它可能有點比你更需要的，但其漂亮和清晰。

Answer 3

嘗試：

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 4

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

或

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

Answer 5

查詢：

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)