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 ( name login PK status etc. ) table status ( status relation label definition PK 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 ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings