Can I have a foreign key referencing a column in a view in SQL Server?

Question

In SQL Server 2008 and given

TableA(A_ID, A_Data)
TableB(B_ID, B_Data)
ViewC(A_or_B_ID, A_or_B_Data)

is it possible to define TableZ(

Answer 1

There is another option. Treat TableA and TableB as subclasses of a new table called TablePrime. Adjust TableB's ID values so they do not coincide with TableA's ID values. Make the ID in TablePrime the PK and insert all of TableA's and TableB's (adjusted) IDs into TablePrime. Make TableA and TableB have FK relationships on their PK to the same ID in TablePrime.

You now have the supertype/subtype pattern, and can make constraints to TablePrime (when you want either-A-or-B) or one of the individual tables (when you want only A or only B).

If you need more details please ask. There are variations that will let you make sure A and B are mutually exclusive, or maybe the thing you're working with can be both at the same time. It's best to formalize that in the FKs if possible.