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 .
sh@TESTDB> SELECT cust_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,MIDPOINT+100 AS "MAX
2 LOWER LIMIT"
3 FROM customers;
SELECT cust_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,MIDPOINT+100 AS "MAX
*
ERROR at line 1:
ORA-00904: "MIDPOINT": invalid identifier
报错，select中不应该用别名来用在表达式里
sh@TESTDB> SELECT cust_last_name AS "NAME", cust_credit_limit/2 AS MIDPOINT,cust_credit_limit/2+100 AS "MAX LOWER LIMIT"
2 FROM customers WHERE ROWNUM<6;
NAME MIDPOINT MAX LOWER LIMIT
-------------------------------------------------- ---------- ---------------
Ruddy 750 850
Ruddy 3500 3600
Ruddy 5500 5600
Ruddy 750 850
Ruddy 4500 4600
此题答案选A