Q. CUSTOMER (CID, NAME, STREET, CITY, STATE, AGE) SALE (PID, CID, DATE, COST) PART (PID, PNAME, COLOR)

The meaning of these relations is straightforward; for example, SALE has one tuple for every part sold to a customer. Primary key attributes are underlined. For instance, PID and CID together form the primary key of relation SALE. SALE.PID is a foreign key that refers to PART.PID, while SALE.CID is a foreign key that refers to CUSTOMER.CID.

Write SQL statements for the following retrieval and update operations.

1. Retrieve the names of all the customers from the city of "Trenton' who bought a part at a cost less than $50. No duplicates should appear in the answer.
2. Retrieve the names of red parts bought by a customer who is younger than 40 and from a customer who is older than 40.
3. Delete all parts that are never bought by a customer from "Trenton" (this is a data change statement).
4. Retrieve the names of the customers who never bought a green part.
5. Retrieve the names of the customers who bought every red part.