1. LEFT OUTER JOIN:左外關(guān)聯(lián) 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); 等價于 SELECT e.last_name, e.department_id, d.department_name FROM employees e, departments d WHERE e.department_id=d.department_id(+); 結(jié)果為:所有員工及對應(yīng)部門的記錄，包括沒有對應(yīng)部門編號department_id的員工記錄。 2. RIGHT OUTER JOIN:右外關(guān)聯(lián) 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); 等價于 SELECT e.last_name, e.department_id, d.department_name FROM employees e, departments d WHERE e.department_id(+)=d.department_id; 結(jié)果為:所有員工及對應(yīng)部門的記錄，包括沒有任何員工的部門記錄。 3. FULL OUTER JOIN:全外關(guān)聯(lián) 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); 結(jié)果為:所有員工及對應(yīng)部門的記錄，包括沒有對應(yīng)部門編號department_id的員工記錄和沒有任何員工的部門記錄。
