Re: Unique index vs. unique constraint

From: Connor McDonald <connor_mcdonald_at_yahoo.com>
Date: Wed, 01 Sep 1999 19:29:32 +0800
Message-ID: <37CD0E1C.78F9@yahoo.com>

Richard Gaston wrote:
>
> I think unique constraints are implemented as unique indexes in oracle.
> Oracle will create a unique index for the column(s) you declare unique in a
> constraint. So apparently, there's no real difference between the two.
>
> As to why you'd prefer one over the other, I don't know. Taste?
>
> Michael Hjorth <michael_hjorth_at_my-deja.com> wrote in message
> news:7q2vo5$c0g$1_at_nnrp1.deja.com...
> > What is the functional difference between a unique index and a unique
> > constraint?
> > I know the latter has a constraint as well as the index, but apparently
> > it enforces the same restrictions on the database as the unique index.
> > Or did I get it wrong?
> > Why would I prefer one over the other in a particular case?
> >
> > Thank you for any comments.
> >
> > Michael.
> >
> >
> > Sent via Deja.com http://www.deja.com/
> > Share what you know. Learn what you don't.

It is possible to implement a unique constraint with a NON unique index in 8.1, thus making them different...

Also with unique constraints you can make them deferrable and other nice things that cannot be done with a unique index.

Cheers

Connor McDonald
"These views mine, no-one elses etc etc" connor_mcdonald_at_yahoo.com

"Some days you're the pigeon, and some days you're the statue." Received on Wed Sep 01 1999 - 06:29:32 CDT