Christian Schröder wrote: > How can I enforce these constraints? I submit that you should rethink your database schema and properly normalize it. You are attempting to retool the algebra that underlies the SQL functionalities into doing something they are not designed to do, and you will, even if you manage to solve this particular problem, be in a constant battle against the database system to get your application to behave in a consistent manner. A first step in that direction would be to rethink the apparently troublesome use of null values. -- Peter Eisentraut http://developer.postgresql.org/~petere/
