On 10/30/24 00:19, Tom Lane wrote:
Andrei Lepikhov <lepi...@gmail.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
