Feedback-ID: ie3de48e3:Fastmail
Date: Tue, 21 Oct 2025 10:23:27 +0300
From: =?utf-8?Q?=C3=81lvaro?= Herrera <alvherre@kurilemu.de>
To: Paul Austin <paul.austin@automutatio.com>
Cc: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Subject: Re: Extend CREATE POLICY to add IF EXISTS
Message-ID: <202510210716.4cr5qkq2z2mj@alvherre.pgsql>
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On 2025-Oct-20, Paul Austin wrote:

> Adrian,
> 
> The drop policy IF EXISTS does work.
> 
> But it would be nice to have the IF NOT EXISTS on CREATE POLICY so I
> don't need to do a drop and create.

How would CREATE IF NOT EXISTS handle the case of an existing policy
that doesn't match the one you want?  I think it would just silently not
do anything, and in that case you can't really rely on it, can you?  So
your script would have to extract the current policy, compare with the
one you want (how?) and then maybe drop it and create it anew, or leave
it alone.  Is this really useful?

I think what you'd really appreciate is CREATE OR REPLACE: if the
policy exists and matches the one you ask for, then don't do anything;
but otherwise throw it away and create it anew.  We have this for views,
and it allows for things like adding more columns than the original view
had.

BTW, the pattern DROP IF EXISTS / CREATE is a bit nasty, because there
exists a period in between where no policy exists, which could be a
security hole.  Unless you use an explicit transaction block.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"I love the Postgres community. It's all about doing things _properly_. :-)"
(David Garamond)