Database question

[Ray Cote]

>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