59. View the Exhibit and examine the data in the PRODUCTS table.
You need to display product names from the PRODUCTS table that belong to the 'Software/Other '
category with minimum prices as either $2000 or $4000 and no unit of measure.
You issue the following query:
SQL>SELECT prod_name, prod_category, prod_min_price
FROM products
WHERE prod_category LIKE '%Other%' AND (prod_min_price = 2000 OR
prod_min_price = 4000) AND prod_unit_of_measure <> '';
Which statement is true regarding the above query?
A. It executes successfully but returns no result.
B. It executes successfully and returns the required result.
C. It generates an error because the condition specified for PROD_UNIT_OF_MEASURE is not valid.
D. It generates an error because the condition specified for the PROD_CATEGORY column is not valid.
Answer: A
答案解析：
实验验证：
SELECT prod_name, prod_category, prod_min_price
2 FROM products
3 WHERE prod_category LIKE '%Other%' AND (prod_min_price = 2000 OR
4 prod_min_price = 4000) AND prod_unit_of_measure <> '';
no rows selected
prod_unit_of_measure <> ''; 应该改为is not null
因为prod_unit_of_measure <> ''该条件为假，’’相当于NULL，所以会导致该WHERE子句里所有AND连接的值为假，
虽然执行成功但不会返回结果，正确的条件应该是prod_unit_of_measure is not null。