SQL 分组后获取其中一个字段最大值的整条记录

【原文】http://blog.csdn.net/sz_bdqn/article/details/7259738

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--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