QUESTION NO: 30
View the Exhibit and examine the description for the CUSTOMERS table.
You want to update the CUST_CREDIT_LIMIT column to NULL for all the customers, where
CUST_INCOME_LEVEL has NULL in the CUSTOMERS table. Which SQL statement will
accomplish the task?
A.UPDATE customers SET cust_credit_limit = NULL WHERE CUST_INCOME_LEVEL = NULL;
B.UPDATE customers SET cust_credit_limit = NULL WHERE cust_income_level IS NULL;
C.UPDATE customers SET cust_credit_limit = TO_NUMBER(NULL) WHERE cust_income_level = TO_NUMBER(NULL);
D.UPDATE customers SET cust_credit_limit = TO_NUMBER(' ',9999) WHERE cust_income_level IS NULL;
Answer: B
答案解析：
参考：163：http://blog.csdn.net/rlhua/article/details/12886715
Explanation: