How do you deal with polymorphism in a database?

Question

Example

I have Person, SpecialPerson, and User. Person and SpecialPerson are just people - they don\

Answer 1

What I'm going to say here is going to send database architects into conniptions but here goes:

Consider a database view as the equivalent of an interface definition. And a table is the equivalent of a class.

So in your example, all 3 person classes will implement the IPerson interface. So you have 3 tables - one for each of 'User', 'Person' and 'SpecialPerson'.

Then have a view 'PersonView' or whatever that selects the common properties (as defined by your 'interface') from all 3 tables into the single view. Use a 'PersonType' column in this view to store the actual type of the person being stored.

So when you're running a query that can be operated on any type of person, just query the PersonView view.