Really Simple question about making a pop up menu
I have a simple question.
I am creating an Invoice database with the products being previously defined. I have typed out the few hundred items into the Inventory table of the database. The customer is primarily using this item on their Ipad and I'm deciding (but leaning towards) a pop-up menu over a drop down box. My question is that I want to have the product they select to appear only once on the Invoice. The customer has usually 40-50 items per invoice and I don't want them to accidentally list a product twice on there. I know how to do this in MySQL and C+ but am a little lost on how to do this in FMP. Hopefully it is easy.