取时间最大的一条记录

A表
id          title
a1            a1

b表
id          Aid      name      time
b1         a1         u             2017-5-6
b2         a1         x              2017-7-8
b3         a1         z              2017-2-9

显示成

b2
a1 x
2017-07-08 

if not object_id(N'Tempdb..#A') is null

    drop table #A

Go

Create table #A([id] nvarchar(22),[title] nvarchar(22))

Insert #A

select N'a1',N'a1'

GO

if not object_id(N'Tempdb..#B') is null

    drop table #B

Go

Create table #B([id] nvarchar(22),[Aid] nvarchar(22),[name] nvarchar(21),[time] DateTIME)

Insert #B

select N'b1',N'a1',N'u','2017-5-6' union all

select N'b2',N'a1',N'x','2017-7-8' union all

select N'b3',N'a1',N'z','2017-2-9'

Go

select * from  #A

select * from  #B

;WITH cte AS (

SELECT  * ,

        ROW_NUMBER() OVER ( PARTITION BY Aid ORDER BY time DESC ) AS num

FROM    #B 

)

SELECT  cte.id ,

        cte.Aid ,

        cte.name ,

        cte.time

FROM    cte

        JOIN #A ON #A.id = cte.Aid

WHERE   cte.num = 1;