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【071题库】最新OCP-071考试题库解析-第31题

【071题库】最新OCP-071考试题库解析-第31题

071考试是OCP考试科目的一种,由于071考题多变,我们专门收集整理了最新的考试题库,并对这些考题进行讲解,希望可以帮助广大考生。

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071题库-第31题、choose the best answer:

Examine the structure of the EMPLOYEES table:

There is a parent/child relationship between EMPLOYEE_ID and MANAGER_ID.

You want to display the name, joining date, and manager for all the employees.

Newly hired employees are yet to be assigned a department or a manager. For them, 'No Manager' should be displayed in the MANAGER column.

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(+);

)

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