当前位置: 首页 > 图文教程 > 数据库 > MSSQL > 一条语句简单解决“每个Y的最新X”的经典sql语句

MSSQL
精通数据库系列之入门：基础篇1
剖析SQL Server 2005查询通知之基础篇
用sp_lock诊断SQL Sever的性能问题
测试SQL Server业务规则链接方法
解析SQL Server数据应用在不同的数据库中
如何使用SQL Server数据库中查询累计值
逐行扫描 为你讲解几个基本SQLPLUS命令
教你一招：MSSQL数据库索引的应用
确定几个SQL Server栏中的最大值
SQL Server 2005分析服务 统一整合视图
如何使用SQL Server嵌套子查询
用TableDiff产生SQL Server同步脚本
小型商业应用选SQL Server还是Access
用SQL Server Having计算列和平均值
SQL Server 2005基于消息的应用程序介绍
在SQL Server实例之间传输登录和密码
SQL Server 2005深层工具和运行时间集
SQL Server数据库增强版备份体验
使用SQL Server 2000日志转移实现高可用性
浅谈Linq To Sql集成数据库语言的优劣

No. « 32 33 34 35 »

技术文章搜索

关键字

MSSQL 中的 一条语句简单解决“每个Y的最新X”的经典sql语句

出处:互联网   整理: 软晨网（RuanChen.com）   发布: 2009-09-13   浏览: 150 ::
收藏到网摘: n/a

“每个Y的最新X”是一个经典的SQL问题，工作中经常碰到。当然不是“按Y分组求最新的X值”那么简单，要求最新X的那条记录或主键ID。用一条SQL语句可以简单的解决此问题。 生成实例表和数据：
复制代码 代码如下:

/****** 创建表 ******/
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[Table]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[Table]
GO
Create TABLE [dbo].[Table] (
[ID] [int] IDENTITY (1, 1) NOT NULL ,
[Y] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[X] [smalldatetime] NOT NULL
) ON [PRIMARY]
GO
--插入数据
Insert INTO [Table](Y, X) values('CCC', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('AAA', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('AAA', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('BBB', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('BBB', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('BBB', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('CCC', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('AAA', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('CCC', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('DDD', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('DDD', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('DDD', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('EEE', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('EEE', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('EEE', '2007-03-03 03:03:03')
GO
/****** 创建表 ******/
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[Table]') and OBJECTPROPERTY(id, N'IsUserTable') = 1)
drop table [dbo].[Table]
GO
Create TABLE [dbo].[Table] (
[ID] [int] IDENTITY (1, 1) NOT NULL ,
[Y] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NOT NULL ,
[X] [smalldatetime] NOT NULL
) ON [PRIMARY]
GO
--插入数据
Insert INTO [Table](Y, X) values('CCC', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('AAA', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('AAA', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('BBB', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('BBB', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('BBB', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('CCC', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('AAA', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('CCC', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('DDD', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('DDD', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('DDD', '2007-03-03 03:03:03')
Insert INTO [Table](Y, X) values('EEE', '2007-01-01 01:01:01')
Insert INTO [Table](Y, X) values('EEE', '2007-02-02 02:02:02')
Insert INTO [Table](Y, X) values('EEE', '2007-03-03 03:03:03')

GO解决“每个Y的最新X”经典SQL问题：以下几种方法真是八仙过海
复制代码 代码如下:

Select ID, Y, X
FROM [Table] T1
Where (NOT EXISTS
(Select 1
FROM [Table] T2
Where (T2.Y = T1 .Y) AND (T2.X > T1 .X or
T2.X = T1 .X AND T2.ID > T1 .ID)))
/*****************************************************************************/
Select *
FROM [Table]
Where ID IN
(Select MAX(T1.ID)
FROM [Table] T1 JOIN
(Select y, MAX(x) x
FROM [Table]
GROUP BY y) T2 ON T1.Y = T2.Y AND T1.x = T2.x
GROUP BY T1.y)
/*****************************************************************************/
Select T .ID, T .Y, T .X
FROM [Table] T INNER JOIN
(Select MAX(T1.ID) AS ID
FROM [Table] T1 JOIN
(Select y, MAX(x) x
FROM [Table]
GROUP BY y) T2 ON T1.Y = T2.Y AND T1.x = T2.x
GROUP BY T1.y) T2 ON T .ID = T2.ID
/*****************************************************************************/
Select *
FROM [Table] T1
Where ID IN
(Select TOP 1 ID
FROM [Table]
Where Y = T1.Y
orDER BY X DESC)
/*****************************************************************************/
Select *
FROM [Table] T1
Where (ID =
(Select TOP 1 ID
FROM [Table]
Where Y = T1.Y
orDER BY X DESC, ID DESC))
/*****************************************************************************/
/*****************************************************************************/
Select ID, Y, X
FROM [Table] T1
Where (NOT EXISTS
(Select 1
FROM [Table] T2
Where (T2.Y = T1 .Y) AND (T2.X > T1 .X or
T2.X = T1 .X AND T2.ID > T1 .ID)))
/*****************************************************************************/
Select *
FROM [Table]
Where ID IN
(Select MAX(T1.ID)
FROM [Table] T1 JOIN
(Select y, MAX(x) x
FROM [Table]
GROUP BY y) T2 ON T1.Y = T2.Y AND T1.x = T2.x
GROUP BY T1.y)
/*****************************************************************************/
Select T .ID, T .Y, T .X
FROM [Table] T INNER JOIN
(Select MAX(T1.ID) AS ID
FROM [Table] T1 JOIN
(Select y, MAX(x) x
FROM [Table]
GROUP BY y) T2 ON T1.Y = T2.Y AND T1.x = T2.x
GROUP BY T1.y) T2 ON T .ID = T2.ID
/*****************************************************************************/
Select *
FROM [Table] T1
Where ID IN
(Select TOP 1 ID
FROM [Table]
Where Y = T1.Y
orDER BY X DESC)
/*****************************************************************************/
Select *
FROM [Table] T1
Where (ID =
(Select TOP 1 ID
FROM [Table]
Where Y = T1.Y
orDER BY X DESC, ID DESC))

/*****************************************************************************
/效率嘛,在不同的字段建立索引速度都不尽相同,使用者见仁见智了.
第一种方法速度在各方面都不错,而且在Y列在建立索引，可以大大优化查询速度。