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From: Álvaro Herrera <alvherre@kurilemu.de>
To: pgsql-hackers@lists.postgresql.org
Subject: Re: Fix ALTER COLUMN ... DROP EXPRESSSION with subpartitions
Date: Tue, 4 Aug 2026 09:26:16 +0200
Message-ID: <anGRnFgKM6RFmGLm@alvherre.pgsql> (raw)
In-Reply-To: <DHMT78XOD8BK.341V3H87KZ7NO@gmail.com>

Hello Alberto,

On 2026-Apr-07, Alberto Piai wrote:

> While working on [0], I noticed that DROP EXPRESSION currently refuses
> to be applied to inheritance trees of depth > 2, e.g. when there are
> subpartitions.

Yep, confirmed.

> PFA a fix for this and a test case.
> 
> I added the test case to generated_stored.sql,

Looks good.  I pushed your fix, with two minor changes:
1. acquiring a lock in the find_inheritance_children() call is
   confusing and unnecessary, because ATSimpleRecursion already did it,
   so I removed that by passing NoLock.

2. I removed the comment that suggested that the functionality could be
   implemented with some effort.  This was foreclosed by 8bf6ec3ba3a4, 
   so the comment is false and wrong.

I also moved the test to the exact spot where ALTER TABLE DROP
EXPRESSION is being tested.  That gave me the perfect placement for the
corresponding test for the legacy-inheritance part of the functionality.

The backpatch was pretty straightforward (mostly because git-cherry-pick
figured out by itself that it needed to apply the generated_stored.sql
patch to generated.sql at the point where it was renamed.)

I think you didn't add a commitfest entry for this.  Please don't forget
to create one for every patch that you submit; otherwise they're likely
to fall through the cracks.  (Though these days the CF process seems
more and more to be a mostly useless, abandoned chore.)

Thanks!

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
<Schwern> It does it in a really, really complicated way
<crab> why does it need to be complicated?
<Schwern> Because it's MakeMaker.

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