OCP 1Z0 051 15

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 .

别名不能在同一范围内被另一列引用。

正确的写法应该是嵌套一层

SQL> show user;
User is "test"

SQL>
SQL> CREATE TABLE customers(cust_no,cust_name,cust_city,cust_credit_limit) AS
2  SELECT 101,'KING','NEW_YORK',100000 FROM DUAL UNION ALL
3  SELECT 102,'GREEN','BOSTON',150000 FROM DUAL UNION ALL
4  SELECT 103,'SCOTT','LONDON',NULL FROM DUAL UNION ALL
5  SELECT 104,'SMITH','BOSTON',NULL FROM DUAL;
Table created

SQL> SELECT "NAME",MIDPOINT,MIDPOINT+100  AS  "MAX
2  LOWER LIMIT"
3  FROM
4  (
5  SELECT  cust_name  AS  "NAME",  cust_credit_limit/2  AS  MIDPOINT
6  FROM customers);
NAME    MIDPOINT MAX
LOWER LIMIT
----- ---------- ---------------
KING       50000           50100
GREEN      75000           75100
SCOTT
SMITH

Answer: A