t sql 读出每组的前n个

http://topic.csdn.net/u/20100113/17/b52a1ef4-54a8-4333-8119-a161869c1eef.html
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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
/*
ID   GID         Author &