The Stock of the book needs to be updated correspondingly after a customer has made an order, or a customer has cancelled an order. It can be accomplished by using trigger. You are asked to implement...

The Stock of the book needs to be updated correspondingly after a customer has made an order, or a customer has cancelled an order. It can be accomplished by using trigger. You are asked to implement a trigger which needs to take following into consideration:
a. The trigger needs to be fired after a new row has been inserted into table Orders, or after a row has been deleted from table Orders which indicates an order has been cancelled
b. Each order may contain multiple books in ORDERTITEMS table
            You also need to write SQL statement or/and PL/SQL code to demonstrate that the implemented trigger accomplishes the business logic