Is it a good idea to use a personal number as a primary key for a customer table?
Some good criteria for choosing or designing keys are: Simplicity, Stability and Familiarity but first you need to understand the fundamental business requirement your key is supposed to address. Ask yourself how you intend to identify customers in your business processes. Assuming you have a requirement to identify customers and Customer Number is the means your business will use to do that then it makes perfect sense as a key in your customer table - not necessarily the only key, but certainly a key of that table.