--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：