Re: BUG #16303: A condtion whether an index-only scan is possible includes a wrong

On Sunday, March 15, 2020, Horimoto Yasuhiro <horimoto@clear-code.com>
wrote:

> I send a patch for this problem.!
>
> From: PG Bug reporting form <noreply@postgresql.org>
> Subject: BUG #16303: A condtion whether an index-only scan is possible
> includes a wrong
> Date: Mon, 16 Mar 2020 06:02:25 +0000
>
> > I think that the condition of whether an index-only scan is possible
> > includes a wrong.
> >
> > For example, in the following case, the index has no data to return.
> Because
> > the query doesn't use specify columns.
> > However, the query planner choice index-only scan.
>
>

> > In my opinion, we expected that the query planner doesn't choose an
> > index-only scan in the above case.
> >
>
>
I don't see a behavioral bug here. I would expect that any index would be
an acceptable match for a query whose set of return columns is the empty
set. The empty set is a subset of all sets.

David J.