Re: Account for cost and selectivity of HAVING quals

On Wed, Nov 1, 2017 at 8:41 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> writes:
>> On Wed, Nov 1, 2017 at 3:15 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> here's a patch to fix the planner so that eval costs and selectivity of
>>> HAVING quals are factored into the appropriate plan node numbers.
>>> ...
>>> + /* Add cost of qual, if any --- but we ignore its selectivity */
>
>> And may be we should try to explain why can we ignore selectivity.
>> Similarly for the changes in create_minmaxagg_path().
>
> I'm sure you realize that's because the estimate is already just one
> row ... but sure, we can spell that out.
>

+1. That would be helpful.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company