查每个分组前N条记录

--? Author: liangCK 小梁

--? Title : 查每个分组前N条记录

--? Date? : 2008-11-13 17:19:23

---------------------------------

?

--> 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','胡百敬','SQLServer2005性能调校',' 2008-03-22 ' UNION ALL

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

SELECT '004','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','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','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','赵松涛','SQLServer2005系统管理实录',' 2008-10-01 ' UNION ALL

SELECT '010','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

/*

?

ID?? GID???????? Author??????????????????????? Title??????????????????????????? Date

---- ----------- ----------------------------- ------------------------- -----------------------

003? 1?????????? 格罗夫Groff.J.R.???????????????? SQL完全手册????????????????? 2009-07-01 00:00:00.000

004? 1?????????? KalenDelaney????????????????? SQLServer2005技术内幕存储引擎?? 2008-08-01 00:00:00.000

005? 2?????????? Alex.Kriegel.Boris.M.Trukhnov?? SQL宝典?????????????????????? 2007-10-05 00:00:00.000

007? 2?????????? 胡百敬?????????????????????????? SQLServer2005数据库开发详解? 2008-06-15 00:00:00.000

009? 3?????????? 赵松涛?????????????????????????? SQLServer2005系统管理实录??? 2008-10-01 00:00:00.000

010? 3?????????? 黄占涛?????????????????????????? SQL技术手册????????????????? 2006-01-01 00:00:00.000

?

(6 行受影响)

*/

（编辑：李大同）

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