Re: Allowing additional commas between columns, and at the end of the SELECT clause

On Mon, 13 May 2024 at 10:42, Artur Formella <artur(dot)formella3(at)gmail(dot)com> wrote:
> Motivation:
> Commas of this type are allowed in many programming languages, in some
> it is even recommended to use them at the ends of lists or objects.

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.

> Accepted:
> SELECT 1,;
> SELECT 1,,,,,;
> SELECT *, from information_schema.sql_features;
> (...) RETURNING a,,b,c,;
>
> Not accepted:
> SELECT ,;
> SELECT ,1;
> SELECT ,,,;
>
> Advantages:
> - simplifies the creation and debugging of queries by reducing the most
> common syntax error,
> - eliminates the need to use the popular `1::int as dummy` at the end of
> a SELECT list,

This is the first time I've heard of this `1 as dummy`.

> - simplifies query generators,
> - the query is still deterministic,

What part of a query would (or would not) be deterministic? I don't
think I understand the potential concern here. Is it about whether the
statement can be parsed deterministically?

> Disadvantages:
> - counting of returned columns can be difficult,
> - syntax checkers will still report errors,
> - probably not SQL standard compliant,

I'd argue you better raise this with the standard committee if this
isn't compliant. I don't see enough added value to break standard
compliance here, especially when the standard may at some point allow
only a single trailing comma (and not arbitrarily many).

> What do you think?

Do you expect `SELECT 1,,,,,,,` to have an equivalent query identifier
to `SELECT 1;` in pg_stat_statements? Why, or why not?

Overall, I don't think unlimited commas is a good feature. A trailing
comma in the select list would be less problematic, but I'd still want
to follow the standard first and foremost.

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)