Re: Normalization, Natural Keys, Surrogate Keys

Bernard Peek (bap_at_shrdlu.com) wrote:
: In message <c1ec9b8f.0205241023.ebb99a0_at_posting.google.com>, Kai Ponte
: <cybermusicdude_at_aol.com> writes

: >> Having a surrogate primary key shouldn't let you off the hook. As a
: >> rule of thumb, you always HAVE TO HAVE an alternate UNIQUE constraint.
: >I respectfully disagree with "always have to have." Yes, it may often
: >be necessary, but not always.

: Can you suggest a situation where you do not need a unique constraint in
: addition to the surrogate?

The inability to provide a unique constraint (other than a surrogate) is exactly one of the reasons why data may need a surrogate.

This happens when using old data. In addition to it being impractical to fix all old data before loading it into a new system, it may also be questionable to do so because the existing data may be a historical record, such as a license, which cannot be "corrected" within the framework of the application even if it appears to be wrong. Received on Tue May 28 2002 - 16:38:47 CDT