OCP-1Z0-051-题目解析-第15题

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15. View the Exhibit and examine the data in the CUSTOMERS table.

Evaluate the following query:

SQL> SELECT cust_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,MIDPOINT+100 AS "MAX LOWER LIMIT" FROM customers;

The above query produces an error on execution.

What is the reason for the error?

（问上面这条sql语句产生错误的原因是什么？）

A. An alias cannot be used in an expression.
B. The a lias NAME should not be enclosed with in double quotation marks .
C. The MIDPOINT+100 expression gives an error because CUST_CREDIT_LIMIT contains NULL values.
D. The a lias MIDPOINT should be enclosed with in double quotation marks for the CUST_CREDIT_LIMIT/2 expression .

Answer: A

题目解析：

A：别名不可用于Select列表中的表达式（正确）
B：别名不可以放在双引号里（错误，别名放在双引号里表示别名的显示格式和输入一致）
C: MIDPOINT+100表达式出错，因为CUST_CREDIT_LIMIT包含空值（错误，这与空值无关）
D: CUST_CREDIT_LIMIT/2表达式的别名MIDPOINT需要加上双引号（错误，不加双引号表示别名的显示都是大写字母）

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