---------------------------------
--?Author: liangCK 小梁
--?Title : 查每個(gè)分組前N條記錄
--?Date : 2008-11-13 17:19:23
---------------------------------

--> 生成測試數(shù)據(jù): #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','深入淺出SQLServer2005開發(fā)管理與應(yīng)用實(shí)例','2008-05-10'?UNION?ALL
SELECT?'002',1,'胡百敬','SQLServer2005性能調(diào)校','2008-03-22'?UNION?ALL
SELECT?'003',1,'格羅夫Groff.J.R.','SQL完全手冊','2009-07-01'?UNION?ALL
SELECT?'004',1,'KalenDelaney','SQLServer2005技術(shù)內(nèi)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(chǎn)品研發(fā)中心','SQLServer2000高級管理與開發(fā)','2007-09-10'?UNION?ALL
SELECT?'007',2,'胡百敬','SQLServer2005數(shù)據(jù)庫開發(fā)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(tǒng)管理實(shí)錄','2008-10-01'?UNION?ALL
SELECT?'010',3,'黃占濤','SQL技術(shù)手冊','2006-01-01'

--SQL查詢?nèi)缦?

--按GID分組,查每個(gè)分組中Date最新的前2條記錄


--1.字段ID唯一時(shí):
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不唯一時(shí):
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(jìn)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


--結(jié)果
/*

ID?? GID???????? Author??????????????????????? Title?????????????????????????????????? Date
---- ----------- ----------------------------- --------------------------------------- -----------------------
003 1?????????? 格羅夫Groff.J.R.???????????????? SQL完全手冊???????????????????????????????? 2009-07-01 00:00:00.000
004 1?????????? KalenDelaney????????????????? SQLServer2005技術(shù)內(nèi)幕存儲引擎?????????????????? 2008-08-01 00:00:00.000
005 2?????????? Alex.Kriegel.Boris.M.Trukhnov SQL寶典?????????????????????????????????? 2007-10-05 00:00:00.000
007 2?????????? 胡百敬?????????????????????????? SQLServer2005數(shù)據(jù)庫開發(fā)詳解??????????????????? 2008-06-15 00:00:00.000
009 3?????????? 趙松濤?????????????????????????? SQLServer2005系統(tǒng)管理實(shí)錄???????????????????? 2008-10-01 00:00:00.000
010 3?????????? 黃占濤?????????????????????????? SQL技術(shù)手冊???????????????????????????????? 2006-01-01 00:00:00.000

(6 行受影響)
*/

--得到每組前幾條數(shù)據(jù)
--假設(shè)每組Col1中， Col3不會重復(fù)

--建立測試環(huán)境
Create?Table?TEST
(Col1?Varchar(10),
Col2?Varchar(10),
Col3?Int)
--插入數(shù)據(jù)
Insert?TEST?Select?'BD1V','Label',?4
Union?All?Select?'BD1V',?'BATT',?2
Union?All?Select?'BD1V',?'ODD',?3
Union?All?Select?'BD1V',?'HDD',?5
Union?All?Select?'BD1V',?'LCD',?1
Union?All?Select?'BD1W','HDD',?3
Union?All?Select?'BD1W','RAM',?8
Union?All?Select?'BD1W','TP CABLE',?5
Union?All?Select?'BD1W','LCD',?6
Union?All?Select?'BD1W','Label',?2
Union?All?Select?'BL3',?'LCD CABLE',?7
Union?All?Select?'BL3',?'LABEL',?6
Union?All?Select?'BL3',?'LCD',?5
Union?All?Select?'BL3',?'RAM',?1
Union?All?Select?'BL3D',?'Label',?4
GO
--測試
--方法一：
Select?Col1, Col2, Col3?From?TEST A
Where?(Select?Count(*)?From?TEST?Where?Col1?=?A.Col1?And?Col3?>?A.Col3)?<?3
Order?By?Col1, Col3?Desc
--方法二：
Select?Col1, Col2, Col3?From?TEST A
Where?Exists?(Select?Count(*)?From?TEST?Where?Col1?=?A.Col1?And?Col3?>?A.Col3?Having?Count(*)?<?3)
Order?By?Col1, Col3?Desc
--方法三：
Select?Col1, Col2, Col3?From?TEST A
Where?Col3?In?(Select?TOP?3?Col3?From?TEST?Where?Col1?=?A.Col1?Order?By?Col3?Desc)
Order?By?Col1, Col3?Desc
GO
--刪除測試環(huán)境
Drop?Table?TEST
--結(jié)果
/*
Col1 Col2?? Col3
BD1V HDD 5
BD1V Label 4
BD1V ODD 3
BD1W RAM 8
BD1W LCD?? 6
BD1W TP CABLE 5
BL3 LCD CABLE 7
BL3 LABEL 6
BL3 LCD?? 5
BL3D Label 4
*/

轉(zhuǎn)載于:https://www.cnblogs.com/thanks/archive/2011/12/14/2287608.html

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