SQL在分组查询时，怎么获取最新一条记录

sql如何分组选择显示最新的一条数据

首先,该问题对应的SQL如下

select 采购类别,客户,订货总额

from (select 采购类别,客户,订货总额,

row_number() over(partition by 采购类别 order by 订货总额 desc) rn

from table_name) awhere rn<=2

其次,常用数据库比如Oracle和Sqlserver都有特定函数完成分组排序的功能,如果需要显示并列的情况可以用下面另外的2个.

分别有3个类似函数：

row_number() over

这个函数不需要考虑是否并列，哪怕根据条件查询出来的数值相同也会进行连续排名。也是最常用的函数，排序结果类似于1,2,3,4,5

rank() over

查出指定条件后进行一个排名，但是有一个特点。假如是对学生排名，那么实用这个函数，成绩相同的两名是并列。排序结果类似于1,2,2,4,5

dense_rank() over

比较特殊，排序结果类似于1,2,2,3,4

--查每个分组前N条记录

-->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 AuthorTitle Date

---- ----------- ----------------------------- --------------------------------------- -----------------------

003 1 格罗夫Groff.J.R. SQL完全手册 2009-07-01 00:00:00.000

004 1 KalenDelaney SQLServer2005技术内幕存储引擎 2008-08-01 00:00:00.000

005 2 Alex.Kriegel.Boris.M.Trukhnov SQL宝典 2007-10-05 00:00:00.000

007 2 胡百敬 SQLServer2005数据库开发详解2008-06-15 00:00:00.000

009 3 赵松涛 SQLServer2005系统管理实录 2008-10-01 00:00:00.000

010 3 黄占涛 SQL技术手册 2006-01-01 00:00:00.000

(6 行受影响)

*/

--得到每组前几条数据

--假设每组Col1中， Col3不会重复

--建立测试环境

Create Table TEST

(Col1 Varchar(10),

Col2 Varchar(10),

Col3 Int)

--插入数据

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

--测试

--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

--删除测试环境

Drop Table TEST

--结果

/*

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

*/

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