1Z0-051 QUETION 15 别名的用法

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本文探讨了一段包含错误的SQL查询语句，并分析了错误的原因。指出在SELECT语句中直接使用别名会导致语法错误，并给出了具体的错误示例。

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