Feedback-ID: i1ff147bf:Fastmail
From: =?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= <ilmari@ilmari.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>,  Artur Formella
 <artur.formella3@gmail.com>,  pgsql-hackers@postgresql.org
Subject: Re: Allowing additional commas between columns, and at the end of
 the SELECT clause
References: <0368c60f-abe2-4f5f-972d-7cd1e6db2382@gmail.com>
	<CAEze2WhL_A9QO1xHQnEoYN1g5wsigqrL2+FLELcjFwaA-nP-Ug@mail.gmail.com>
	<87bk59hp5o.fsf@wibble.ilmari.org> <738732.1715609494@sss.pgh.pa.us>
Date: Mon, 13 May 2024 17:35:42 +0100
In-Reply-To: <738732.1715609494@sss.pgh.pa.us> (Tom Lane's message of "Mon, 13
	May 2024 10:11:34 -0400")
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Tom Lane <tgl@sss.pgh.pa.us> writes:

> =?utf-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= <ilmari@ilmari.org> writes:
>> Matthias van de Meent <boekewurm+postgres@gmail.com> writes:
>>> Single trailing commas are a feature that's more and more common in
>>> languages, yes, but arbitrary excess commas is new to me. Could you
>>> provide some examples of popular languages which have that, as I can't
>>> think of any.
>
>> The only one I can think of is Perl, which I'm not sure counts as
>> popular any more.  JavaScript allows consecutive commas in array
>> literals, but they're not no-ops, they create empty array slots:
>
> I'm fairly down on this idea for SQL, because I think it creates
> ambiguity for the ROW() constructor syntax.  That is:
>
> 	(x,y) is understood to be shorthand for ROW(x,y)
>
> 	(x) is not ROW(x), it's just x
>
> 	(x,) means what?

Python has a similar issue: (x, y) is a tuple, but (x) is just x, and
they use the trailing comma to disambiguate, so (x,) creates a
single-item tuple.  AFAIK it's the only place where the trailing comma
is significant.

> I realize the original proposal intended to restrict the legality of
> excess commas to only a couple of places, but to me that just flags
> it as a kluge.  ROW(...) ought to work pretty much the same as a
> SELECT list.

Yeah, a more principled approach would be to not special-case target
lists, but to allow one (and only one) trailing comma everywhere:
select, order by, group by, array constructors, row constructors,
everything that looks like a function call, etc.

> As already mentioned, if you can get some variant of this through the
> SQL standards process, we'll probably adopt it.  But I doubt that we
> want to get out front of the committee in this area.

Agreed.

> 			regards, tom lane

- ilmari