From: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
To: David G. Johnston <david.g.johnston@gmail.com>
Cc: pgsql-sql@lists.postgresql.org <pgsql-sql@lists.postgresql.org>
Subject: RE: unique index with several columns
Date: Fri, 4 Mar 2022 16:11:31 +0000
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In-Reply-To: <CAKFQuwa4dELLaEdm2UsZK-LyRA08VYOYQZyxNs8zF25nYzgv3w@mail.gmail.com>
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<CAKFQuwa4dELLaEdm2UsZK-LyRA08VYOYQZyxNs8zF25nYzgv3w@mail.gmail.com>
Yes, it helps, thank you.
But I have many tables with many indexes and many columns!
Tons of combinations… ☹
From: David G. Johnston <david.g.johnston@gmail.com>
Sent: Friday, March 4, 2022 4:32 PM
To: Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com>
Cc: pgsql-sql@lists.postgresql.org
Subject: Re: unique index with several columns
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On Fri, Mar 4, 2022 at 8:07 AM Voillequin, Jean-Marc <Jean-Marc.Voillequin@moodys.com<mailto:Jean-Marc.Voillequin@moodys.com>> wrote:
When one of the field is null, PG considers that the tuple is not the same:
('a',null) is not equal to ('a',null)
So, the unique constraint is not violated in PG.
But is there a way to have the same feature than Oracle?
I already tried with:
create unique index idx on t(coalesce(c1,''),coalesce(c2,''))
But in this case, I cannot insert several (null,null) without raising a duplicate key error.
You just said you wanted nulls to be considered equal to each other...
Not tested but these should work in conjunction with each other:
CREATE UNIQUE INDEX idx ON t (c1, c2) WHERE c1 IS NOT NULL AND c2 IS NOT NULL;
CREATE UNIQUE INDEX idx2 ON t (c1) WHERE c2 IS NULL AND c1 IS NOT NULL;
CREATE UNIQUE INDEX idx3 ON t (c2) WHERE c1 IS NULL AND c2 IS NOT NULL;
--CREATE INDEX idx4 ON t (c1, c2) WHERE c1 IS NULL AND c2 IS NULL; (pointless...but symmetric with the others)
Hopefully this helps.
David J.
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To: pgsql-sql@postgresql.org
Cc: Jean-Marc.Voillequin@moodys.com, david.g.johnston@gmail.com, pgsql-sql@lists.postgresql.org
Subject: RE: unique index with several columns
In-Reply-To: <MN2PR20MB2735EB2F5DA362B53277BE11BE059@MN2PR20MB2735.namprd20.prod.outlook.com>
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