Re: Normalization questions...

Pavel,

Sometimes you "discover" keys, rather than "inventing" them.

In your case, the combination uid, gid can only occur once the junction table. A uid might appear in several rows. A gid might appear in several rows. But, in combination, they are unique.

You can treat (uid, gid) as the primary key. Most DBMSes will let you declare a compound primary key.

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Regards,
    David Cressey
    www.dcressey.com