Hello Nick,

> what, if any, is the effective difference?
>
> I recall that a unique constraint is enforced via an index so does it
> ever matter which is used?

Yes, Foreign Key Constraints can "point" to a Unique Constraint, but
not to a Unique Index.

Martijn Tonies
Database Workbench - tool for InterBase, Firebird, MySQL, NexusDB, Oracle &
MS SQL Server
Upscene Productions
http://www.upscene.com
My thoughts:
http://blog.upscene.com/martijn/
Database development questions? Check the forum!
http://www.databasedevelopmentforum.com