【分享】查每个分组前N条记录收藏（转）
from:http://blog.csdn.net/liangCK/archive/2008/11/13/3292540.aspx
自己又对这个有了深的了解，分享下
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-- Author: liangCK 小梁4
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-- Title : 查每个分组前N条记录6
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-- Date : 2008-11-13 17:19:238
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--> 生成测试数据: #T14
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IF OBJECT_ID('tempdb.dbo.#T') IS NOT NULL DROP TABLE #T16
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CREATE TABLE #T (ID VARCHAR(3),GID INT,Author VARCHAR(29),Title VARCHAR(39),Date DATETIME)18
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INSERT INTO #T20
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SELECT '001',1,'邹建','深入浅出SQLServer2005开发管理与应用实例','2008-05-10' UNION ALL22
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SELECT '002',1,'胡百敬','SQLServer2005性能调校','2008-03-22' UNION ALL24
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SELECT '003',1,'格罗夫Groff.J.R.','SQL完全手册','2009-07-01' UNION ALL26
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SELECT '004',1,'KalenDelaney','SQLServer2005技术内幕存储引擎','2008-08-01' UNION ALL28
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SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL宝典','2007-10-05' UNION ALL30
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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 ALL32
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SELECT '007',2,'胡百敬','SQLServer2005数据库开发详解','2008-06-15' UNION ALL34
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SELECT '008',3,'陈浩奎','SQLServer2000存储过程与XML编程','2005-09-01' UNION ALL36
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SELECT '009',3,'赵松涛','SQLServer2005系统管理实录','2008-10-01' UNION ALL38
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SELECT '010',3,'黄占涛','SQL技术手册','2006-01-01'40
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--SQL查询如下:44
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--按GID分组,查每个分组中Date最新的前2条记录48
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--1.字段ID唯一时:52
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SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)54
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--2.如果ID不唯一时:58
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SELECT * FROM #T AS T WHERE 2>(SELECT COUNT(*) FROM #T WHERE GID=T.GID AND Date>T.Date)60
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--SQL Server 2005 使用新方法64
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--3.使用ROW_NUMBER()进行排位分组68
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SELECT ID,GID,Author,Title,Date70
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FROM72
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(74
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SELECT rid=ROW_NUMBER() OVER(PARTITION BY GID ORDER BY Date DESC),*76
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FROM #T78
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) AS T80
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WHERE rid<=282
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--4.使用APPLY86
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SELECT DISTINCT b.*88
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FROM #T AS a90
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CROSS APPLY92
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(94
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SELECT TOP(2) * FROM #T WHERE a.GID=GID ORDER BY Date DESC96
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) AS b98
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--结果104
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/**//*106
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ID GID Author Title Date110
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---- ----------- ----------------------------- ------------------------- -----------------------112
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003 1 格罗夫Groff.J.R. SQL完全手册 2009-07-01 00:00:00.000114
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004 1 KalenDelaney SQLServer2005技术内幕存储引擎 2008-08-01 00:00:00.000116
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005 2 Alex.Kriegel.Boris.M.Trukhnov SQL宝典 2007-10-05 00:00:00.000118
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007 2 胡百敬 SQLServer2005数据库开发详解 2008-06-15 00:00:00.000120
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009 3 赵松涛 SQLServer2005系统管理实录 2008-10-01 00:00:00.000122
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010 3 黄占涛 SQL技术手册 2006-01-01 00:00:00.000124
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(6 行受影响)128
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*/130
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