Oracle中的外连接语句

对于外连接，oracle中可以使用“(+)”来表示，9i可以使用left/right/full outer join，下面将配合实例一一介绍。

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。