Problem
Relational Algebra use relational algebra notation, no sql quieries
The primary keys are bold. All attributes are of type string if not indicated otherwise. [Hint: Use multi-step and multi-line queries to ease the formulation of queries. Use the rename operator ρ to give intermediate query results a name (some textbooks use the equivalent '←' notation). Aggregate functions as you can find them defined in some textbooks are not allowed.
a) Book(bID, title, author, publisher, year, price)
b) Customer(cID, name, SSN, gender, email)
c) CreditCard(ccID, cID, number, exprDate)
d) BookOrder(oID, bID, ccID, quantity: integer, date)
1. Find the titles of books that were ordered by the customers John or Jane. Assume John and Jane are unique.
2. Find the dates of the orders when John's credit card was used.
3. Find the names of publishers whose books are not sold yet.
4. Find the information of customers(name and email) who have credit cards that have been never used. Show their never-used credit card numbers as well. Assume a customer can have multiple credit cards. The customers have ordered before(with other credit cards).
5. Find the names of customers who have orders a 'DB' book more than once.
6. Find the information of the most expensive 'DB' book. List the title, author, publisher, year, and price.