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SQL Server中交叉联接的用法详解

时间：2021-04-22来源：www.pcxitongcheng.com作者：电脑系统城

今天给大家介绍SQLServer中交叉联接的用法，希望对大家能有所帮助!

1、交叉联接(cross join)的概念

交叉联接是联接查询的第一个阶段，它对两个数据表进行笛卡尔积。即第一张数据表每一行与第二张表的所有行进行联接，生成结果集的大小等于T1*T2。

1	`select` `*` `from` `t1` `cross` `join` `t2`

2、交叉联接的语法格式

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5 select * from t1 cross join t2;--常用写法
select * from t1, t2;-- SQL:1989的规范
select * from t1 cross join t2
where t1.col1=t2.col2;--等价于内部联接
select * from t1 inner join t2 on t1.col1=t2.col2

3、交叉查询的使用场景

3.1 交叉联接可以查询全部数据

-- 示例

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57 -- 员工表
CREATE TABLE [dbo].[EmpInfo](
[empId] [int] IDENTITY(1,1) NOT NULL,
[empNo] [varchar](20) NULL,
[empName] [nvarchar](20) NULL,
CONSTRAINT [PK_EmpInfo] PRIMARY KEY CLUSTERED
(
[empId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF
, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

-- 奖金表
CREATE TABLE [dbo].[SalaryInfo](
[id] [int] IDENTITY(1,1) NOT NULL,
[empId] [int] NULL,
[salary] [decimal](18, 2) NULL,
[seasons] [varchar](20) NULL,
CONSTRAINT [PK_SalaryInfo] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF
, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
-- 季度表
CREATE TABLE [dbo].[Seasons](
[name] [nchar](10) NULL
) ON [PRIMARY]

GO
SET IDENTITY_INSERT [dbo].[EmpInfo] ON

INSERT [dbo].[EmpInfo] ([empId], [empNo], [empName]) VALUES (1, N'A001', N'王强')
INSERT [dbo].[EmpInfo] ([empId], [empNo], [empName]) VALUES (2, N'A002', N'李明')
INSERT [dbo].[EmpInfo] ([empId], [empNo], [empName]) VALUES (3, N'A003', N'张三')

INSERT [dbo].[SalaryInfo] ([id], [empId], [salary], [seasons])
VALUES (1, 1, CAST(3000.00 AS Decimal(18, 2)), N'第一季度')
INSERT [dbo].[SalaryInfo] ([id], [empId], [salary], [seasons])
VALUES (2, 3, CAST(5000.00 AS Decimal(18, 2)), N'第一季度')
INSERT [dbo].[SalaryInfo] ([id], [empId], [salary], [seasons])
VALUES (3, 1, CAST(3500.00 AS Decimal(18, 2)), N'第二季度')
INSERT [dbo].[SalaryInfo] ([id], [empId], [salary], [seasons])
VALUES (4, 3, CAST(3000.00 AS Decimal(18, 2)), N'第二季度 ')
INSERT [dbo].[SalaryInfo] ([id], [empId], [salary], [seasons])
VALUES (5, 2, CAST(4500.00 AS Decimal(18, 2)), N'第二季度')

INSERT [dbo].[Seasons] ([name]) VALUES (N'第一季度')
INSERT [dbo].[Seasons] ([name]) VALUES (N'第二季度')
INSERT [dbo].[Seasons] ([name]) VALUES (N'第三季度')
INSERT [dbo].[Seasons] ([name]) VALUES (N'第四季度')

-- 查询每个人每个季度的奖金情况如果奖金不存在则为0
SELECT a.empName,b.name seasons ,isnull(c.salary,0) salary
FROM EmpInfo a
CROSS JOIN Seasons b
LEFT OUTER JOIN SalaryInfo c ON a.empId=c.empId AND b.name=c.seasons