ORACLE表连接方法

一般的相等连接：select * from a, b where a.id = b.id;这个就属于内连接。对于外连接：Oracle中可以使用“(+) ”来表示，9i可以使用LEFT/RIGHT/FULL OUTER JOINLEFT OUTER JOIN：左外关联SELECT e.last_name, e.department_id, d.department_nameFROM employees eLEFT OUTER JOIN departments dON (e.department_id = d.department_id);等价于SELECT e.last_name, e.department_id, d.department_nameFROM employees e, departments dWHERE 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。RIGHT OUTER JOIN：右外关联SELECT e.last_name, e.department_id, d.department_nameFROM employees eRIGHT OUTER JOIN departments dON (e.department_id = d.department_id);等价于SELECT e.last_name, e.department_id, d.department_nameFROM employees e, departments dWHERE 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。FULL OUTER JOIN：全外关联SELECT e.last_name, e.department_id, d.department_nameFROM employees eFULL OUTER JOIN departments dON (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。ORACLE8i是不直接支持完全外连接的语法，也就是说不能在左右两个表上同时加上(+)，下面是在ORACLE8i可以参考的完全外连接语法select t1.id,t2.id from table1 t1,table t2 where t1.id=t2.id(+)unionselect t1.id,t2.id from table1 t1,table t2 where t1.id(+)=t2.id