| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Steve Rogerson <steve(dot)pg(at)yewtc(dot)demon(dot)co(dot)uk> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Unique constraints and indexes. |
| Date: | 2016-01-05 20:13:52 |
| Message-ID: | CAKFQuwa3=5=Wpn65+2rm-QhN-BHQa9WHak2OCW9qSikh33Rgqw@mail.gmail.com |
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| Lists: | pgsql-general |
On Tuesday, January 5, 2016, Steve Rogerson <steve(dot)pg(at)yewtc(dot)demon(dot)co(dot)uk>
wrote:
> On 05/01/16 19:47, Tom Lane wrote:
> > Steve Rogerson <steve(dot)pg(at)yewtc(dot)demon(dot)co(dot)uk <javascript:;>> writes:
> >> Is this a bug? I create a "unique" index, directly but it doesn't add a
> unique
> >> constraint. Add a unique constraint and it adds the index and the
> constraint.
> >
> > That's operating as designed. A unique constraint needs an index,
> > but not vice versa.
>
>
> I can see that might be plausible , hence the question but as a "unique
> index"
> imposes as constraint they seem equivalent. What's the functional
> difference
> between the two situations?
>
>
I suspect it has to do with partial unique indexes.
David J.
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