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Subject: Re: docs: clarify ALTER TABLE behavior on partitioned tables
From: Chao Li <li.evan.chao@gmail.com>
In-Reply-To: <CAKFQuwbUVLeeooQWc0TY7NJS05RexG_fOY5cz2S4H3sDGKQ_qA@mail.gmail.com>
Date: Mon, 26 Jan 2026 12:16:24 +0800
Cc: Zsolt Parragi <zsolt.parragi@percona.com>,
 Postgres hackers <pgsql-hackers@lists.postgresql.org>,
 Amit Kapila <amit.kapila16@gmail.com>
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To: "David G. Johnston" <david.g.johnston@gmail.com>
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> On Jan 24, 2026, at 09:16, David G. Johnston =
<david.g.johnston@gmail.com> wrote:
>=20
>=20
> On Fri, Jan 23, 2026 at 5:57=E2=80=AFPM David G. Johnston =
<david.g.johnston@gmail.com> wrote:
>=20
> "A nonrecursive DROP COLUMN (i.e., ALTER TABLE ONLY ... DROP COLUMN)
> never removes any descendant columns, but instead marks them as
> independently defined rather than inherited."
>=20
> This part is now undocumented, it was only mentioned in this =
paragraph.
>=20
> True, it's left implied instead of explicitly stated.  Any column that =
exists on a child but not the parent is by definition "independently =
defined".  So if either ONLY is supplied or the rules for cascading =
delete are not met the result is children with independently defined =
columns with that name.
>=20
>  The original note was wrong anyway for the two-parent case - the =
second parent prevents the marking as independent when the first =
parent's column is dropped.
>=20
> Decided to test this one and I see the original wording was correct =
and we will need to keep a note that in the two-parent ONLY case the =
un-dropped children are marked both dependent and independent.
>=20
> Change:
>=20
>      <para>
>       For inheritance setups, a descendant column is removed only if =
both of the
>       following are true: this is the only parent defining the column, =
and the column
>       was never independently defined in the descendant.
>      </para>
>=20
> To:
>=20
> "For inheritance setups, a descendant column is removed only if all =
the following are true: ONLY is not specified, no other parent defines =
the column, and the column is not marked as having been independent.  =
Otherwise, the descendant column is instead marked as having been =
independent.
>=20
> If we think that deserves a bit longer explanation about that/why/how =
a column can be both dependent and "having been independent" we should =
cross-reference to a more appropriate location.  Here we just state this =
is one way that condition can materialize.
>=20
> David J.
>=20

Thanks a lot for the test. Included in v7.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/