Re: unique index with several columns

From: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
To: Klaus Kaisersberger <woodconsult(at)outlook(dot)de>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alexey M Boltenkov <padrebolt(at)yandex(dot)ru>, "Voillequin, Jean-Marc" <Jean-Marc(dot)Voillequin(at)moodys(dot)com>, "pgsql-sql(at)lists(dot)postgresql(dot)org" <pgsql-sql(at)lists(dot)postgresql(dot)org>
Subject: Re: unique index with several columns
Date: 2022-03-04 19:06:04
Message-ID: CAKFQuwZuLqsmaFKHVbKry6v4tYHReVp_z6bgvr23vJXU1_OnRw@mail.gmail.com
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On Fri, Mar 4, 2022 at 11:57 AM Klaus Kaisersberger <woodconsult(at)outlook(dot)de>
wrote:

> This should solve the task:
>
> create unique index idx on t ((
> case
> when c1 is null and c2 is null then null
> when c1 is null and c2 is not null then '{c2}'
> when c1 is not null and c2 is null then '{c1}'
> else '{c1,c2}'
> end));
>
>
I'm not sure what your '{c1}' syntax means but I'll take it you are
suggesting to construct an array. This seems to fail quite easily if the
values of c1 and c2 overlap.

David J.

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