We enter our vendor invoices into our system and we have issues with duplicate invoices being entered. I wanted to make the vendor invoice number field (text) unique BUT what if there was the same invoice number for more than on vendor? (believe me it does happen with vendors who have four or three digit invoice numbers.)

I then thought of a way to create a formula that would concatenate the vendor account code with the vendor invoice number. That would then be a very unique number. BUT I don't think that you can make formulas unique.

What can I do?