Re: multi column foreign key for implicitly unique columns

Jan,

>      In the case that a table constraint is a referential constraint,
>      the table is referred to as the referencing table. The referenced
>      columns of a referential constraint shall be the unique columns of
>      some unique constraint of the referenced table.

Missed that one.  Interesting.  AFAIK, the uniqueness of referenced columns is 
NOT a requirement of Relaitonal Algebra.   So why does SQL require it?

Maybe I'll ask Joe Celko after he finishes moving to Austin.

I have my own issue that forced me to use triggers.   Given:

table users (namelogin PKstatusetc. )

table status (statusrelationlabeldefinitionPK status, relation )

the relationship is:
users.status = status.status AND status.relation = 'users';

This is a mathematically definable constraint, but there is no way in standard 
SQL to create an FK for it.    This is one of the places I point to whenever 
we have the "SQL is imperfectly relational" discussion.    

-- 
Josh Berkus
Aglio Database Solutions
San Francisco