OCP认证051考试题库：11g-v9.02-第163题
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163. 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
试题解析：
题意要求：更新CUSTOMERS表中所有customers的CUST_CREDIT_LIMIT值，当CUST_INCOME_LEVEL为NULL时更新CUST_CREDIT_LIMIT为空。
AC的where条件都为假，所有都不更新。
D的set语句有语法问题，故错误。
