OCP-1Z0-051 补充题库 第4题 聚合函数的使用

一、原题

See the Exhibit and examine the structure and data in the INVOICE table:
Exhibit:

Which two sql statements would executes successfully? (Choose two.)
A. SELECT MAX(inv_date),MIN(cust_id) FROM invoice;
B. SELECT MAX(AVG(SYSDATE - inv_date)) FROM invoice;
C. SELECT AVG(inv_date) FROM invoice;
D. SELECT AVG(inv_date - SYSDATE),AVG(inv_amt) FROM invoice;

答案: A,D

二、题目翻译

看下面INVOICE表的结构：
哪两个sql会执行成功（选择两项）?

三、题目解析

B选项不正确，SYSDATE - inv_date的结果是数字，这里AVG的结果就只有一条记录了，再求MAX，就没意义了，这句会报错。 C选面不正确，inv_date是日期类型，AVG求日期的平均值，会报错。