如何在group by子句中查找每个组的最大日期时间值

Question

user_id UserName    created_on                 dateTime
189 essa amuel      2011-08-26 16:31:13.750    2011-11-08 10:13:49.000
189 essa amuel      2011-08-26 16:31:13.750    2011-11-14 16:38:54.000
19  kessa samuel    2011-08-26 16:31:13.750    2011-11-18 12:56:50.000
19  kessa samuel    2011-08-26 16:31:13.750    2011-11-22 14:12:56.000

How to get user latest login time for each user by group by clause on userid

Answer 1

SELECT user_id, UserName, last_login = MAX([datetime])
FROM dbo.table
GROUP BY user_id, UserName;

As an aside, you shouldn't use reserved words like datetime as column names.

Answer 2

SELECT USERNAME, MAX([dateTime]) FROM tablename GROUP BY USERNAME

不是吗？