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Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter? - Mailing list pgsql-general

From David G. Johnston
Subject Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter?
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Msg-id CAKFQuwa9ZER4yPfXgHAoX18O_qTj07ZVKvkAPYVeajYyPzTd5w@mail.gmail.com
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In response to [GENERAL] How to create unique index on multiple columns where the combination doesn't matter?  (Glen Huang <hey.hgl@gmail.com>)
Responses Re: [GENERAL] How to create unique index on multiple columns wherethe combination doesn't matter?
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On Wed, Mar 22, 2017 at 9:54 AM, Glen Huang <hey.hgl@gmail.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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