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groupby以后取每组前n行

-----------------------------------  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: #TIF OBJECT_ID(tempdb.dbo.#T) IS NOT NULL DROP TABLE #TCREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME)INSERT INTO #TSELECT 001,1,邹建,深入浅出SQLServer2005开发管理与应用实例,2008-05-10 UNION ALLSELECT 002,1,胡百敬,SQLServer2005性能调校,2008-03-22 UNION ALLSELECT 003,1,格罗夫Groff.J.R.,SQL完全手册,2009-07-01 UNION ALLSELECT 004,1,KalenDelaney,SQLServer2005技术内幕存储引擎,2008-08-01 UNION ALLSELECT 005,2,Alex.Kriegel.Boris.M.Trukhnov,SQL宝典,2007-10-05 UNION ALLSELECT 006,2,飞思科技产品研发中心,SQLServer2000高级管理与开发,2007-09-10 UNION ALLSELECT 007,2,胡百敬,SQLServer2005数据库开发详解,2008-06-15 UNION ALLSELECT 008,3,陈浩奎,SQLServer2000存储过程与XML编程,2005-09-01 UNION ALLSELECT 009,3,赵松涛,SQLServer2005系统管理实录,2008-10-01 UNION ALLSELECT 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,DateFROM(   SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),*   FROM #T) AS TWHERE rid<=2--4.使用APPLYSELECT DISTINCT b.*FROM #T AS aCROSS 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 00:00:00.000004  1           KalenDelaney                  SQLServer2005技术内幕存储引擎                   2008-08-01 00:00:00.000005  2           Alex.Kriegel.Boris.M.Trukhnov SQL宝典                                   2007-10-05 00:00:00.000007  2           胡百敬                           SQLServer2005数据库开发详解                    2008-06-15 00:00:00.000009  3           赵松涛                           SQLServer2005系统管理实录                     2008-10-01 00:00:00.000010  3           黄占涛                           SQL技术手册                                 2006-01-01 00:00:00.000(6 行受影响)*/