1Z0-051 QUETION 15 别名的用法

QUESTION 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?

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 .

答案：A

解析：

别名不能在SELECT语句中直接使用。

SQL> SELECT cust_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,MIDPOINT+100 A
S "MAX
2 LOWER LIMIT"
3 FROM customers;
SELECT cust_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,MIDPOINT+100 AS "MA
X
*
ERROR at line 1:
ORA-00904: "MIDPOINT": invalid identifier