65、(22-16) choose the best answer:
The CUSTOMERS table has the following structure:
You need to write a query that does the following tasks:
- Display the first name and tax amount of the customers. Tax is 5% of their credit limit.
- Only those customers whose income level has a value should be considered.
- Customers whose tax amount is null should not be considered.
Which statement accomplishes all the required tasks?
A) SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE (cust_income_level,tax_amount) IS NOT NULL;
B) SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE cust_income_level IS NOT NULL AND
cust_credit_limit IS NOT NULL;
C) SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE cust_income_level <> NULL AND
tax_amount <> NULL;
D) SELECT cust_first_name, cust_credit_limit * .05 AS TAX_AMOUNT
FROM customers
WHERE cust_income_level IS NOT NULL AND
tax_amount IS NOT NULL;
Answer:B
(解析:条件语句中不能用别名当做条件,该题的题意是税额不能为 0,所以只要 cust_credit_limit 不为 0,则保证税额不会为 0
原文地址:https://blog.51cto.com/13854012/2359400