Re: Conditional Relationships ?

>> I'm curious as to how one would go about setting up and enforcing a
Conditional Relationship. <<

Try a better example; a student is either a foreign students or a domestic student. Unlike your orders and order details example, the two cases are clearly not related to each other.

In Standard SQL-92, you would use a CREATE ASSERTION statement, which is like CHECK() constraint at the schema level. Here is one way

CREATE ASSERTION StudentClassification
CHECK (((SELECT student_nbr FROM DomesticStudents

        UNION ALL 
        SELECT student_nbr FROM ForeignStudents)
        EXCEPT 
        SELECT student_nbr FROM Students) IS NULL);