You are maintaining a Microsoft SQL Server database that stores order information for an online store website. The database contains a table that is defined by the following Transact-SQL statement:
You need to ensure that purchase order numbers are used only for a single order.
What should you do?
A. Create a new CLUSTERED constraint on the PurchaseOrderNumber column.
B. Create a new UNIQUE constraint on the PurchaseOrderNumber column.
C. Create a new PRIMARY constraint on the PurchaseOrderNumber column.
D. Create a new FOREIGN KEY constraint on the PurchaseOrderNumber column.
