Combination of 2 fields to be the unique record
I am creating a database for an event that has a number of Workshops. I have created these databases: Workshops, Orders, Students, Payments. Because one Order may contain multiple Workshops, and one Workshop may be on multiple Orders, I've created a database called WorkshopOrders, that is linked to the Workshop dbase with a field called Workshop#, and links to the Order dbase with a field called OrderID.
I would like to make it so that the combination of those two fields in the WorkshopsOrders dbase (Workshop# & OrderID) is unique. So that only one combination of Workshop# and OrderID is allowed.
How do I make the combination of those unique? Or am I thinking of it incorrectly?