Message-ID: <9334a884530a0aa56f3a1e7fd24e995c415dab25.camel@cybertec.at>
Subject: Re: About #13489, array dimensions and CREATE TABLE ... LIKE
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Tom Lane <tgl@sss.pgh.pa.us>, Bruce Momjian <bruce@momjian.us>
Cc: Bruno Bonfils <asyd@asyd.net>, PostgreSQL-development
	 <pgsql-hackers@postgresql.org>, Alexey Bashtanov <alexey@brandwatch.com>
Date: Tue, 21 Nov 2023 09:33:18 +0100
In-Reply-To: <1403260.1700532781@sss.pgh.pa.us>
References: <ZD+14YZ4IUue8Rhi@gendo.asyd.net> <ZPuN20z3HcBXdKow@momjian.us>
	 <ZVwI_ozT8z9MCnIZ@momjian.us> <1402391.1700532261@sss.pgh.pa.us>
	 <ZVwQ6Fyh2SghkXja@momjian.us> <1403260.1700532781@sss.pgh.pa.us>
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Precedence: bulk

On Mon, 2023-11-20 at 21:13 -0500, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > On Mon, Nov 20, 2023 at 09:04:21PM -0500, Tom Lane wrote:
> > > Bruce Momjian <bruce@momjian.us> writes:
> > > > An alternate approach would
> > > > be to remove pg_attribute.attndims so we don't even try to preserve=
=20
> > > > dimensionality.
>=20
> > > I could get behind that, perhaps.  It looks like we're not using the
> > > field in any meaningful way, and we could simplify TupleDescInitEntry
> > > and perhaps some other APIs.
>=20
> > So should I work on that patch or do you want to try?  I think we shoul=
d
> > do something.
>=20
> Let's wait for some other opinions, first ...

Looking at the code, I get the impression that we wouldn't lose anything
without "pg_attribute.attndims", so +1 for removing it.

This would call for some documentation.  We should remove most of the
documentation about the non-existing difference between declaring a column
"integer[]", "integer[][]" or "integer[3][3]" and just describe the first
variant in detail, perhaps mentioning that the other notations are
accepted for backward compatibility.

I also think that it would be helpful to emphasize that while dimensionalit=
y
does not matter to a column definition, it matters for individual array val=
ues.
Perhaps it would make sense to recommend a check constraint if one wants
to make sure that an array column should contain only a certain kind of arr=
ay.

Yours,
Laurenz Albe