减少子查询加盟

Question

我很抱歉，这个问题已经被问过的净很多次，但我不明白如何优化我的子查询：

SELECT * 
FROM rp_clientAffectationHistory as T1 
WHERE rp_clientAffectationHistoryID in (SELECT MAX(rp_clientAffectationHistoryID) 
     FROM rp_clientAffectationHistory as T2 
GROUP BY `rp_clientID`) 
AND `rp_userID` = 57 

我有许多重复的条目相同的“rp_clientID”，我只想要最新的rp_clientAffectationHistoryID记录。

非常感谢

Answer 1

你需要的是这样的：

SELECT * 
    FROM Rp_Clientaffectationhistory AS T1 
left join Rp_Clientaffectationhistory as T2 on (T1.Rp_Clientid = T2.Rp_Clientid) and T1.Rp_Clientaffectationhistoryid < T2.Rp_Clientaffectationhistoryid 
where T2.Rp_Clientaffectationhistoryid is null 
and T1.Rp_Userid = 57 

帮助？

Answer 2

我猜你想只有一个，每rp_clientID入门 -

你错过的一件事是检查rp_clientID内查询中 -

SELECT * 
    FROM Rp_Clientaffectationhistory AS T1 
WHERE Rp_Clientaffectationhistoryid IN 
     (SELECT MAX(Rp_Clientaffectationhistoryid) 
      FROM Rp_Clientaffectationhistory AS T2 
     WHERE T1.Rp_Clientid = T2.Rp_Clientid 
     GROUP BY Rp_Clientid) 
    AND Rp_Userid = 57 

是你在找什么？

Answer 3

对于SQL Server，请尝试：

SELECT * FROM(
    SELECT *, ROW_NUMBER() over (partition by rp_userID order by rp_clientAffectationHistoryID desc) Rnum 
    FROM rp_clientAffectationHistory 
    WHERE rp_userID = 57 
)x 
WHERE Rnum=1