Custom Invoice Number from database

Hi everybody!

I love opencart, it has helped me a lot. But I got into a bump with this request I can't seem to answer...

I have a lot of reference numbers from my bank, those numbers identify the payment with the client. The idea is to give every client one of these numbers in order to identify the payment. How can I take the numbers from, say, the database, and assign it to the invoice number?

I'm currently on 1.5.3.1 and the the idea is to automatically assign those invoice numbers, with each purchase.

Thanks!

Is it one number per client?