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Date: Fri, 22 Mar 2019 09:36:14 +0100
From: Christoph Berg <myon@debian.org>
To: thomas@palan.at, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15710: ADD COLUMN IF NOT EXISTS adds constraint anyways
Message-ID: <20190322083614.GA32388@msg.df7cb.de>
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Re: PG Bug reporting form 2019-03-21 <15710-f52bad04543be4cb@postgresql.org>
> CREATE TABLE test (id SERIAL PRIMARY KEY);
> ALTER TABLE test ADD COLUMN IF NOT EXISTS new_column integer UNIQUE;

As a workaround, you can name the constraint:

ALTER TABLE test ADD COLUMN IF NOT EXISTS new_column integer CONSTRAINT id_unique UNIQUE;

Then it won't get added multiple times. (It will still be executed
once, though.)

Christoph