Best way to generate order numbers for an online store?

Question

Every order in my online store has a user-facing order number. I\'m wondering the best way to generate them. Criteria include:

• Short
• Easy to say over the

Answer 1

As a customer I would be happy with:

year-month-day/short_uid

for example:

2009-07-27/KT1E

It gives room for about 33^4 ~ 1mln orders a day.