繁體中文当前位置: 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
- SQL Server 2008批量删除及插入的方法
- SQL Server 2008对T-SQL语言的增强
- SQL Server 2008中不推荐及不支持的功能
- 跟我学SQL：(七)从子表里删除数据
- 如何使用 SQL Server 数据库查询累计值
- 如何使用SQL Server数据库查询累计值
- 选择是否恢复整个SQL Server的方法介绍
- sql server注册表操作相关的几个未公开过程
- 在SQL Server中通过.NET远程的执行SQL文件
- 讲解SQL Server数据库被挂马的解决方案
- SQL Server COALESCE()函数的创新应用
- 教你快速确定SQL Server栏中的最大值
- 避免在 PL/SQL 中使用嵌套游标查询
- 轻松掌握SQL Sever中各种语句的完整语法
- Asp.net编程中的数组基础实例学习
- SQL Server 2005最后升级：SP3年底发布
- SQL Server 2008数据库中的新数据类型
- SQL Server不允许进行远程连接的解决办法
- SQLServer2005 XML在T－SQL中的应用
- 使用SQL Server代理运行CmdExec命令
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: 158 ::
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。
评论 (0) All
