How do I apply subtypes into an SQL Server database?

Question

I am working on a program in which you can register complaints. There are three types of complaints: internal (errors from employees), external (er

Answer 1

In response to you're comment on the accepted answer:

Below is a way to have a check check to ensure only one of the three keys has data:

alter table complaint_master 
    add constraint loc_attribute_has_one_value 
    check ( 
        (case when complaint_employee is null then 0 else 1 end) + 
        (case when complaint_supplier is null then 0 else 1 end) + 
        (case when complaint_external is null then 0 else 1 end)  = 1 
    );