| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Glen Huang <hey(dot)hgl(at)gmail(dot)com> |
| Cc: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: How to create unique index on multiple columns where the combination doesn't matter? |
| Date: | 2017-03-22 17:04:46 |
| Message-ID: | CAKFQuwa9ZER4yPfXgHAoX18O_qTj07ZVKvkAPYVeajYyPzTd5w@mail.gmail.com |
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| Lists: | pgsql-general |
On Wed, Mar 22, 2017 at 9:54 AM, Glen Huang <hey(dot)hgl(at)gmail(dot)com> wrote:
> Hello,
>
> If I have a table like
>
> CREATE TABLE relationship (
> obj1 INTEGER NOT NULL REFERENCES object,
> obj2 INTEGER NOT NULL REFERENCES object,
> obj3 INTEGER NOT NULL REFERENCES object,
> ...
> )
>
> And I want to constrain that if 1,2,3 is already in the table, rows like
> 1,3,2 or 2,1,3 shouldn't be allowed.
>
> Is there a general solution to this problem?
>
> Sorry if the question is too basic, but I couldn't find the answer in the
> doc, at least not in the chapter on unique index.
>
The most direct option to consider is a exclusion constraint.
https://www.postgresql.org/docs/current/static/ddl-constraints.html (bottom
of page)
David J.
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