| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Account for cost and selectivity of HAVING quals |
| Date: | 2017-11-01 15:11:54 |
| Message-ID: | 9878.1509549114@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
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.
regards, tom lane
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