Oracle 外连接实现代码

1. left outer join:左外关联

select e.last_name, e.department_id, d.department_name

from employees e

left outer join departments d

on (e.department_id = d.department_id);

等价于

select e.last_name, e.department_id, d.department_name

from employees e, departments d

where e.department_id=d.department_id(+);

结果为:所有员工及对应部门的记录，包括没有对应部门编号department_id的员工记录。


2. right outer join:右外关联

select e.last_name, e.department_id, d.department_name

from employees e

right outer join departments d

on (e.department_id = d.department_id);

等价于

select e.last_name, e.department_id, d.department_name

from employees e, departments d

where e.department_id(+)=d.department_id;

结果为:所有员工及对应部门的记录，包括没有任何员工的部门记录。


3. full outer join:全外关联
select e.last_name, e.department_id, d.department_name

from employees e

full outer join departments d

on (e.department_id = d.department_id);

结果为:所有员工及对应部门的记录，包括没有对应部门编号department_id的员工记录和没有任何员工的部门记录。