[brantam]

> the correct solution is to use a constraint to enforce the uniqueness

That would of course be correct for a natural key. It seems that you too recommend using natural keys and I agree with you on that point. Natural keys are required so that a database can represent the real world accurately and enforce essential business rules. We all rely on websites to enforce the uniqueness of user names; we all expect our bank to enforce the uniqueness of account numbers.

Those who live in an ivory tower where data quality doesn't matter don't like natural keys; those who write applications that have to work in the real world know how foolish it is to leave out natural keys. Those older and wiser heads will have seen and dealt with the serious practical consequences of shoddy databases where natural keys weren't implemented. I think that is the problem being referred to in this thread.