Multiple foreign keys to a single column

Question

I\'m defining a database for a customer/ order system where there are two highly distinct types of customers. Because they are so different having a single customer table wo

Answer 1

I inherited a SQL Server database where this was done (a single column used in four foreign key relationships with four unrelated tables), so yes, it's possible. My predecessor is gone, though, so I can't ask why he thought it was a good idea.

He used a GUID column ("uniqueidentifier" type) to avoid the ambiguity problem, and he turned off constraint checking on the foreign keys, since it's guaranteed that only one will match. But I can think of lots of reasons that you shouldn't, and I haven't thought of any reasons you should.

Yours does sound like the classical "specialization" problem, typically solved by creating a parent table with the shared customer data, then two child tables that contain the data unique to each class of customer. Your foreign key would then be against the parent customer table, and your determination of which type of customer would be based on which child table had a matching entry.