After preparing the sales order, the sales clerk files one copy of it in the customer
open order file for future reference. Filling the order and getting the product to the customer
may take days or even weeks. Customers frequently contact their suppliers by telephone
to check the status of their orders. To facilitate customer inquiries, the open order
file is often organized alphabetically by customer name. Although customer name is not
an efficient primary key for accessing data, it is often used as a secondary key to crossreference
orders because customers do not always know their account numbers and may
not have copies of their invoices handy. In these situations, the customer file enables the
clerk to find the sales order and respond to the customer’s questions.