oracle各种连接

http://www.itwis.com/html/database/oracle/20080115/847.html

在讲外连接之前，先举例介绍内连接，也就是一般的相等连接。 select * from a, b where a.id = b.id; 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。