However, I want to restrict the member column by restricting the data
in it to also exist *either* in machines.id *OR* in classes.id. The
reason for this is that a class member can either be a machine or
another class (think netgroups here). Does anyone know how to do
this, or if it's even possible?
Triggers.
The design is not relational so you cannot do this with foreign keys.
Foreign keys enforce a column-to-column relationship.
You can do this with a trigger that looks in the two places.
Whenever you run into situations like this, it is always good to
step-back, consider the overall design to see how you ended up in
this situation, and see if a fully-relational design can be
implemented. However, when you really need it this way, triggers are
the way to go.
--Ray
--
Raymond Cote
Appropriate Solutions, Inc.
PO Box 458 ~ Peterborough, NH 03458-0458
Phone: 603.924.6079 ~ Fax: 603.924.8668
rgacote(at)AppropriateSolutions.com
www.AppropriateSolutions.com
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