Add an order to the Order_T table and include a sample value for every attribute.
a. First, look at the data in the Customer_T table and enter an order from any one of those customers.
b. Enter an order from a new customer. Unless you have also inserted information about the new customer in the Customer_T table, your entry of the order data should be rejected. Referential integrity constraints should prevent you from entering an order if there is no information about the customer.