SQL语句查询每个分组的前N条记录的实现方法

--> 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'UNION ALL 
SELECT '010',4,'黄蛋蛋','SQL技术手册蛋蛋','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 
 
select * from #T 
 
--1.字段ID唯一时: 
SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 3 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 
 
 
select * from #T