SQL Server foreign key to multiple tables

Question

I have the following database schema:

members_company1(id, name, ...);
members_company2(id, name, ...);
profiles(memberid, membertypeid, ...);
membertypes(id         


        

Answer 1

A foreign key cannot reference two tables. Assuming you don't want to correct your design by merging members_company1 and members_company2 tables, the best approach would be to:

Add two columns called member_company1_id and member_company2_id to your profiles table and create two foreign keys to the two tables and allow nulls. Then you could add a constraint to ensure 1 of the columns is null and the other is not, at all times.