Which SQL query gets the required output?
A) SELECT e.last_name, e.hire_date, NVL(m.last_name, ‘No Manager‘) Manager
FROM employees e RIGHT OUTER JOIN employees m
ON (e. manager_id = m.employee_id);
B) SELECT e.last_name, e.hire_date, NVL(m.last_name, ‘No Manager‘) Manager
FROM employees e JOIN employees m
ON (e.manager_id = m.employee_id);
C) SELECT e.last_name, e.hire_date, NVL(m.last_name, ‘No Manager‘) Manager
FROM employees e LEFT OUTER JOIN employees m
ON (e.manager_id = m.employee_id);
D) SELECT e.last_name, e.hire_date, NVL(m.last_name, ‘No Manager‘) Manager
FROM employees e NATURAL JOIN employees m
ON (e.manager_id = m.employee_id);
Answer：C
（解析：因为员工 king 是没有经理的，但是也要显示出来，因为是在经理号这边缺少数据，所以这里要用
左外连接。注意左右的区别：
SELECT e.last_name, e.hire_date, NVL(m.last_name, ‘No Manager‘) Manager
FROM employees e , employees m
WHERE e.manager_id = m.employee_id(+);
）
【OCP-12c】CUUG最新考试原题整理及答案（071-10）
原文：http://blog.51cto.com/13854012/2350482