[MSSQL]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','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'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 

查询一个客户对应最后一天下单的的单据信息：

SELECT * FROM (select TD001+'-'+rtrim(TD002)+'-'+TD003 DOCUMENT,TC003,TD004,TD005,TD006,CONVERT(decimal(10,2),TD008) TD008,4),TD011) TD011,TD012 

from COPTC INNER JOIN COPTD ON TC001=TD001 AND TC002=TD002

WHERE TC004='AZ-0005') AS T WHERE 1>(SELECT COUNT(*) FROM (select TD001+'-'+rtrim(TD002)+'-'+TD003 DOCUMENT,TD012 

from COPTC INNER JOIN COPTD ON TC001=TD001 AND TC002=TD002

WHERE TC004='AZ-0005') AS T1 WHERE T1.TD004=T.TD004 AND T1.TC003>T.TC003 AND T1.DOCUMENT>T.DOCUMENT) 

ORDER BY T.TD004,T.TC003 asc

（编辑：李大同）

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