SQL Server中的完全连接(full join)

零、码仙励志

嫉妒別人,不会给自己增加任何的好处。嫉妒別人,也不可能减少別人的成就

一、建库和建表

create database scort
use scort
create table emp
(
	empno int primary key,
	ename nvarchar(10),
	sal int,
	deptno int
)
insert into emp values (7369,'smith',3000,20);
insert into emp values (7499,'allen',1500,50);
insert into emp values (7566,'jones',2000,30);
insert into emp values (7654,'martin',5000,10);
insert into emp values (7698,'blake',1800,30);

create table dept
(
	deptno int primary key,
	dname nvarchar(10),
	loc nvarchar(10)
)
insert into dept values (10,'accounting','new york');
insert into dept values (20,'research','dallas');
insert into dept values (30,'sales','chicago');
insert into dept values (40,'operations','boston');

create table salgrade
(
	grade int primary key,
	lostl int,
	hisal int
)
insert into salgrade values (1,700,1200);
insert into salgrade values (2,1201,1400);
insert into salgrade values (3,1401,2000);
insert into salgrade values (4,2001,3000);
insert into salgrade values (5,3001,6000);

二、完全连接的用法

结果集中包含三部分内容：

1. 两个表中匹配的所有行记录
2. 左表中那些在右表中找不到匹配的行的记录，这些记录的右边全为null
3. 右表中那些在左表中找不到四配的行的记录，这些记录的左边全为null

实例演示：

两张表连接：

select * from emp
	full join dept
	on emp.deptno=dept.deptno

三张表连接：

select * from emp "E"
	full join dept "D"
	on "E".deptno="D".deptno
	full join salgrade "S"
	on "E".sal>"S".lostl and "E".sal<"S".hisal

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