Subject RE: [firebird-support] Unique foreign key for child tables
Author Leyne, Sean
> I have a parent table with multiple child tables.
> Each child row has a foreign key that points to one row in the parent.
> Each parent row must have a child row pointing to it.
> Each parent row can have only child from any of the child tables pointing to it.
> The child is created before the parent.

Since you can't link a child to a parent which doesn't exist, so you could never create a parent which must have a child.

You have a circular dependency so you can't enforce all of those rules via the database.