使用嵌套查询更新语句

Question

我有一张桌子:

mytable:
    id
    userID
    logDate
    lastLogDate

对于该表中的每一行,我想将'lastLogDate'列更新为每个用户的logDate的最大值...

从概念上讲,每个用户都应该有一个lastLogDate =返回的值:

select max(logDate) from mytable group by userID

有人可以帮我写那个更新声明吗？

Answer 1

像这样的东西？

UPDATE mytable SET lastLogDate = t.maxDateForUser  
FROM  
(  
    SELECT userid, MAX(logDate) as maxDateForUser  
    FROM mytable  
    GROUP BY userId  
) t  
WHERE mytable.userid = t.userid

Answer 2

你可以这样做:

UPDATE t
SET t.logDate = t2.LatestDate
FROM YourTable t
INNER JOIN
(
    SELECT userID, MAX(LogDate) LatestDate
    FROM YourTable
    GROUP BY userID
) t2 ON t.userID = t2.userID; 

Answer 3

我不知道我是否理解正确.否则会更具体,但从我得到的,你应该做的事情:

UPDATE `mytable`
SET lastLogDate = (SELECT statement goes here)
WHERE ...