OCP 1Z0 051 14

14.  Using  the  CUSTOMERS  table,   you  need  to  generate  a  report  that  shows  50%  of  each   credit 
amount in each income level. The report should NOT show any repeated credit amounts in each income 
level. 
Which   query would give the required result?
A. SELECT   cust_income_level, DISTINCT cust_credit_limit * 0.50
AS "50% Credit Limit"
FROM customers;
B. SELECT DISTINCT cust_income_level, DISTINCT cust_credit_limit * 0.50
AS "50% Credit Limit"
FROM customers;
C. SELECT DISTINCT cust_income_level , cust_credit_limit * 0.50
AS "50% Credit Limit"
FROM customers;
D. SELECT cust_income_level ,cust_credit_limit * 0.50 AS "50% Credit Limit"
FROM customers;

注意：distinct关键字应该放在select后，所有列之前，不能单独对某一列进行distinct。

a 只对第二列进行distinct， 错

b 每列增加了distinct，错

SELECT cust_income_level, DISTINCT cust_credit_limit * 0.50
AS "50% Credit Limit"
FROM customers
ORA-00936: 缺失表达式

SELECT DISTINCT cust_income_level, DISTINCT cust_credit_limit * 0.50
AS "50% Credit Limit"
FROM customers
ORA-00936: 缺失表达式

d 没有去重。

Answer: C