Given the following SQL statement, which statement is most accurate?
SELECT customer# FROM customers
JOIN orders USING (customer#)
WHERE shipdate-orderdate IN
(SELECT MAX (shipdate-orderdate) FROM orders
WHERE shipdate IS NULL);
a. The SELECT statement fails and returns an Oracle error message.
b. The outer query displays no rows in its results because the subquery passes a NULL value to the outer query.
c. The customer number is displayed for customers whose orders haven’t yet shipped.
d. The customer numbers of all customers who haven’t placed an order are displayed.