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)

*/