oracle中左关联,右关联区别

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Oracle中可以使用“(+) ”来表示，9i可以使用LEFT/RIGHT/FULL OUTER JOIN

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。

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。

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。