【2019年8月版本】OCP 071认证考试最新版本的考试原题-第1题

Choose the best answer.

Exanine the desciption of the EMPLOYEES table:

Nane Null Type

----------------------------------------------------------

EMP_ID NOT NUL NUMBER

EMP_NAME VARCHAR2 (40)

DEPT_ID NUMBER(2)

SALARY NUMBER(8,2)

JOIN_DATE DATE

Which query is valid?

A) SELECT dept_id, join_date, SUM(salary) FROM employees GROUP BY dept_id,join_date;

B) SELECT depe_id,join_date, SUM(salary) FROM employees GROUP BY dept_id:

C) SELECT dept_id,MAX (AVG (salary)) FROM employees GROUP BY dept_id;

D) SELECT dept_ id,AVG (MAX (salary)) FROM employees GROUP BY dapt_id;

Anser:A

(解析：sum 函数如果遇到空值会跳过，不会造成最后的值为空。

其它的查询会出现错误：

SQL> select avg(max(sal)) from emp2 group by deptno;

AVG(MAX(SAL))

-------------

3616.66667

SQL> select deptno,avg(max(sal)) from emp2 group by deptno;

select deptno,avg(max(sal)) from emp2 group by deptno

*

第 1 行出现错误:

ORA-00937: 不是单组分组函数

)