We use poli-morphism with Java classes and I need to duplicate this with a database design... let me explain...

Lets assume:
- we have customers
- customers can either be rich or poor
- we want to store different details for rich and poor customers; i.e.for poor customers we may want to store information about payment problems, unpaid debt, etc. For rich customers we may want to store details about their assets and buying patterns...
- both rich and poor customers buy products

What is the best design you can think off? Can I use MySQL or should I use MS SQL or Oracle?

Thanks for your time and effort