Re: Making the subquery alias optional in the FROM clause

On Mon, 2 Oct 2023 at 00:33, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:

> The only place that exposes the eref's made-up relation name is the
> existing query deparsing code in ruleutils.c, which uniquifies it and
> generates SQL spec-compliant output. For example:
>

I ran into one other place: error messages.

SELECT unnamed_subquery.a
FROM (SELECT 1 AS a)

> ERROR: There is an entry for table "unnamed_subquery", but it cannot be
referenced from this part of the query.invalid reference to FROM-clause
entry for table "unnamed_subquery"

Normally, we would find the cited name somewhere in the query. Confusing.
Notably, the same does not happen for "unnamed_subquery_1":

SELECT unnamed_subquery_1.a
FROM (SELECT 1 AS a), (SELECT 1 AS a)

> ERROR: missing FROM-clause entry for table "unnamed_subquery_1"

That's the message anybody would expect.
Also makes sense, as "uniquification" only happens in the above quoted
case, and all invisible aliases seem to be "unnamed_subquery" at this
point? But a bit confusing on a different level.

Maybe error messages should not be aware of invisible aliases, and just
complain about "missing FROM-clause entry"?
Not sure whether a fix would be easy, nor whether it would be worth the
effort. Just wanted to document the corner case issue in this thread.

Regards
Erwin