Re: Alias of VALUES RTE in explain plan

On 10/30/24 00:19, Tom Lane wrote:
> Andrei Lepikhov <lepihov(at)gmail(dot)com> writes:
>> -- New behavior
>> EXPLAIN (COSTS OFF, VERBOSE)
>> SELECT * FROM (VALUES (4),(2),(3),(1) ORDER BY t1.x LIMIT 2) AS t1(x);
>> SELECT * FROM (VALUES (4),(2),(3),(1) ORDER BY t1.x LIMIT 2) AS t1(x);
>
> After taking a closer look at that, yeah it's new behavior, and
> I'm not sure we want to change it. (The existing behavior is that
> you'd have to write 'column1' or '"*VALUES*".column1' in the
> subquery's ORDER BY.)
>
> This example also violates my argument that the user thinks they
> are attaching the alias directly to VALUES. So what I now think
> is that we ought to tweak the patch so that the parent alias is
> pushed down only when the subquery contains just VALUES, no other
> clauses. Per a look at the grammar, ORDER BY, LIMIT, and FOR
> UPDATE could conceivably appear alongside VALUES; although
> FOR UPDATE would draw "FOR UPDATE cannot be applied to VALUES",
> so maybe we needn't worry about it.
>
> Thoughts?
You have written before that a VALUES alias should be a special case
because it's a 'natural thing'. And I buy it. So, it looks natural to
use this alias everywhere in the query without restrictions. That's why
I provided examples in my previous email to check that it is a full
replacement for the '"*VALUES*".columnN'.

--
regards, Andrei Lepikhov