How to create a unique order number

Question

Algorithmically speaking, how could I generate a unique, human readable, reasonably lengthed - order number for SQL Server column. The only requirement is that it references the Customer Number and can be easily repeated over the phone.

Something like:

• Customer Number - XXXXXXXX - XXXXXXXX

RT65-XXXXXXXX-XXXXXXXX

How would I generate the XXXXXXXX? (Use random alpha-numeric data and then checking to see if it was in fact a duplicate?)

and

What are the best methods/considerations when generating these types of numbers?

How have you done this in your application?

Answer 1

Use an identity column and pad with zeros.

Alter the start and increment values to taste.

Optionally, add a CRC check digit.

Answer 2

Check out these posts, nearly the exact same question. Real good data in both (I've used them before):

A good algorithm for generating an order number

What is the best format for a customer number, order number?