SQL中Left Join 与Right Join 与 Inner Join 与 Full Join的区别
2017-08-06 11:47
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首先看看Left Join 与Right Join 与 Inner Join 与 Full Join对表进行操作后得到的结果。
在数据库中新建两张表,并插入要测试的数据。
新建表:
[sql]
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USE [Test]
GO
/****** 对象: Table [dbo].[EMP] 脚本日期: 06/22/2012 15:37:28 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[EMP](
[ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL,
[CITY] [nchar](10) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
[sql]
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USE [Test]
GO
/****** 对象: Table [dbo].[SAL] 脚本日期: 06/22/2012 15:38:04 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[SAL](
[ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL,
[SALARY] [money] NULL
) ON [PRIMARY]
插入数据得到的表:
EMP表:
SAL表:
左连接
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select * from EMP Left join SAL on EMP.ENAME = SAL.ENAME;
左连接,表EMP是主表,因此查询结果是显示EMP(主表)的全部信息和SAL(附表)与EMP相关的信息。
右连接
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Select * from EMP Right join SAL on EMP.ENAME = SAL.ENAME;
右连接,表SAL是主表,因此查询结果显示SALT(主表)的全部信息和EMP(附表)与SAL想关的信息。
内连接
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SELECT * FROM EMP inner join SAL on EMP.ENAME = SAL.ENAME;
内连接,显示的是连个表相关的信息。
全连接
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SELECT * FROM EMP full join SAL on EMP.ENAME = SAL.ENAME;
全连接,显示两个表所有的信息。
首先看看Left Join 与Right Join 与 Inner Join 与 Full Join对表进行操作后得到的结果。
在数据库中新建两张表,并插入要测试的数据。
新建表:
[sql]
view plain
copy
print?
USE [Test]
GO
/****** 对象: Table [dbo].[EMP] 脚本日期: 06/22/2012 15:37:28 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[EMP](
[ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL,
[CITY] [nchar](10) COLLATE Chinese_PRC_CI_AS NULL
) ON [PRIMARY]
USE [Test] GO /****** 对象: Table [dbo].[EMP] 脚本日期: 06/22/2012 15:37:28 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[EMP]( [ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL, [CITY] [nchar](10) COLLATE Chinese_PRC_CI_AS NULL ) ON [PRIMARY]
[sql]
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USE [Test]
GO
/****** 对象: Table [dbo].[SAL] 脚本日期: 06/22/2012 15:38:04 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[SAL](
[ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL,
[SALARY] [money] NULL
) ON [PRIMARY]
USE [Test] GO /****** 对象: Table [dbo].[SAL] 脚本日期: 06/22/2012 15:38:04 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[SAL]( [ENAME] [nchar](10) COLLATE Chinese_PRC_CI_AS NOT NULL, [SALARY] [money] NULL ) ON [PRIMARY]
插入数据得到的表:
EMP表:
SAL表:
左连接
[sql]
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select * from EMP Left join SAL on EMP.ENAME = SAL.ENAME;
select * from EMP Left join SAL on EMP.ENAME = SAL.ENAME;
左连接,表EMP是主表,因此查询结果是显示EMP(主表)的全部信息和SAL(附表)与EMP相关的信息。
右连接
[sql]
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Select * from EMP Right join SAL on EMP.ENAME = SAL.ENAME;
Select * from EMP Right join SAL on EMP.ENAME = SAL.ENAME;
右连接,表SAL是主表,因此查询结果显示SALT(主表)的全部信息和EMP(附表)与SAL想关的信息。
内连接
[sql]
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copy
print?
SELECT * FROM EMP inner join SAL on EMP.ENAME = SAL.ENAME;
SELECT * FROM EMP inner join SAL on EMP.ENAME = SAL.ENAME;
内连接,显示的是连个表相关的信息。
全连接
[sql]
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copy
print?
SELECT * FROM EMP full join SAL on EMP.ENAME = SAL.ENAME;
SELECT * FROM EMP full join SAL on EMP.ENAME = SAL.ENAME;
全连接,显示两个表所有的信息。
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