近两年来，OCP的考试题库频率变化，不断的增加新考题，071考试就是其中一个，给很多考071的考生造成困扰，对此，我们专门整理了OCP考试里关于071考试的原题，并带上答案，分享给大家。
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071题库汇总-第51题、choose the best answer:
Evaluate the following SQL statement:
SQL> SELECT cust_id, cust_last_name
FROM customers
WHERE cust_credit_limit IN
(select cust_credit_limit
FROM customers
WHERE cust_city ='Singapore');
Which statement is true regarding the above query if one of the values generated by the subquery is NULL?
A) It ignores the NULL value and generates output for the other values produced by the subquery.
B) It produces an error.
C) It generates output for NULL as well as the other values produced by the subquery.
D) It executes but returns no rows.
Answer：A
(解析，子查询中如果有出现某行值为 null，则忽略该行，其它的正常处理，原来 051 的考题。
类似的语句：
select ename from emp where empno in (select mgr from emp);
ENAME
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FORD
BLAKE
KING
JONES
CLARK
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