Re: remove_useless_groupby_columns is too enthusiastic

On Wed, 13 Jul 2022 at 05:31, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I tried the attached quick-hack patch that just prevents
> remove_useless_groupby_columns from removing anything that
> appears in ORDER BY. That successfully fixes the complained-of
> case, and it doesn't change any existing regression test results.
> I'm not sure whether there are any cases that it makes significantly
> worse.

In addition to this, we also do a pre-verification step to see if the
ORDER BY has anything in it that the GROUP BY does not?

I don't think there's any harm in removing the GROUP BY item if the
pre-check finds something extra in ORDER BY since
preprocess_groupclause() is going to fail in that case anyway.

David