sql，groupby之後取每組前三行

--> 生成測試數據: #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,'鄒建','深刻淺出SQLServer2005開發管理與應用實例','2008-05-10' UNION ALL
SELECT '002',1,'胡百敬','SQLServer2005性能調校','2008-03-22' UNION ALL
SELECT '003',1,'格羅夫Groff.J.R.','SQL徹底手冊','2009-07-01' UNION ALL
SELECT '004',1,'KalenDelaney','SQLServer2005技術內幕存儲引擎','2008-08-01' UNION ALL
SELECT '005',2,'Alex.Kriegel.Boris.M.Trukhnov','SQL寶典','2007-10-05' UNION ALL
SELECT '006',2,'飛思科技產品研發中心','SQLServer2000高級管理與開發','2007-09-10' UNION ALL
SELECT '007',2,'胡百敬','SQLServer2005數據庫開發詳解','2008-06-15' UNION ALL
SELECT '008',3,'陳浩奎','SQLServer2000存儲過程與XML編程','2005-09-01' UNION ALL
SELECT '009',3,'趙松濤','SQLServer2005系統管理實錄','2008-10-01' UNION ALL
SELECT '010',3,'黃佔濤','SQL技術手冊','2006-01-01'

--SQL查詢以下:
--按GID分組,查每一個分組中Date最新的前2條記錄

--1.字段ID惟一時:
SELECT * FROM #T AS T WHERE ID IN(SELECT TOP 2 ID FROM #T WHERE GID=T.GID ORDER BY Date DESC)

--2.若是ID不惟一時:
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()進行排位分組
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