--有id,name,createDate的一张表testTable
--根据name分组，获取每组中createDate最大的那条记录（整条）查询出来
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创建一张表，语句如下：
CREATE TABLE [dbo].[testTable]
(
[id] [int] NOT NULL IDENTITY(1, 1),
[name] [nchar] (10) COLLATE Chinese_PRC_CI_AS NULL,
[counts] [int] NULL,
[createDate] [datetime] NULL
)
GO
-- Constraints and Indexes
ALTER TABLE [dbo].[testTable] ADD CONSTRAINT [PK_testTable] PRIMARY KEY CLUSTERED ([id])
GO
插入测试数据：
insert into testTable(id,name,counts,createDate) values(1,'A ',20,'01 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(2,'A ',10,'02 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(3,'B ',20,'03 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(4,'B ',40,'04 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(5,'B ',10,'05 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(6,'C ',20,'06 14 2011 10:52PM')
insert into testTable(id,name,counts,createDate) values(7,'C ',40,'07 14 2011 10:52PM')
查询SQL语句：
select * from (
select id,name,counts,createDate,row_number() over(partition by name order by createDate desc) rn
from testTable
) t where t.rn <=1
结果如下：
