查每个分组前N条记录

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--  Author: liangCK 小梁

--  Title : 查每个分组前N条记录

--  Date  : 2008-11-13 17:19:23

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--> 生成测试数据: #T

IF OBJECT_ID('tempdb.dbo.#T') IS NOT NULL DROP TABLE #T

CREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME)

INSERT INTO #T

SELECT '001',1,'邹建','深入浅出SQLServer2005开发管理与应用实例','2008-05-10' UNION ALL

SELECT '002',1,'胡百敬','SQLServer2005性能调校','2008-03-22' UNION ALL

SELECT '003',1,'格罗夫Groff.J.R.','SQL完全手册','2009-07-01' UNION ALL

SELECT '004',1,'KalenDelaney','SQLServer2005技术内幕存储引擎','2008-08-01' UNION ALL

SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL宝典','2007-10-05' UNION ALL

SELECT '006',2,'飞思科技产品研发中心','SQLServer2000高级管理与开发','2007-09-10' UNION ALL

SELECT '007',2,'胡百敬','SQLServer2005数据库开发详解','2008-06-15' UNION ALL

SELECT '008',3,'陈浩奎','SQLServer2000存储过程与XML编程','2005-09-01' UNION ALL

SELECT '009',3,'赵松涛','SQLServer2005系统管理实录','2008-10-01' UNION ALL

SELECT '010',3,'黄占涛','SQL技术手册','2006-01-01'

--SQL查询如下:

--按GID分组,查每个分组中Date最新的前2条记录

--1.字段ID唯一时:

SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)

--2.如果ID不唯一时:

SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)

--SQL Server 2005 使用新方法

--3.使用ROW_NUMBER()进行排位分组

SELECT ID,GID,Author,Title,Date

FROM

(

   SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),*

   FROM #T

) AS T

WHERE rid<=2

--4.使用APPLY

SELECT DISTINCT b.*

FROM #T AS a

CROSS APPLY

(

    SELECT TOP(2) * FROM #T WHERE a.GID=GID ORDER BY Date DESC

) AS b

--结果