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--测试数据
if not object_id(N'Tempdb..#student') is null
drop table #student
Go
Create table #student([id] int,[CardNum] int,[ClassName] nvarchar(21),[DateTime] Date)
Insert #student
select 1,100,N'a','2017-01-01' union all
select 2,101,N'a','2017-01-02' union all
select 3,110,N'b','2017-01-02' union all
select 4,111,N'b','2017-01-04' union all
select 5,200,N'c','2017-01-02'
Go
--测试数据结束
SELECT COUNT(1) AS 总数 ,
ClassName ,
MAX(DateTime) AS MaxDateTime
FROM #student
GROUP BY ClassName;
select
count(1) as [总数(CardNum)]
,ClassName
,Max([DateTime]) as [Max(DateTime)]
from student
group by ClassName