From: Tom Lane <tgl@sss.pgh.pa.us>
To: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Account for cost and selectivity of HAVING quals
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Comments: In-reply-to Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
	message dated "Wed, 01 Nov 2017 18:06:55 +0530"
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Date: Wed, 01 Nov 2017 11:11:54 -0400
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Ashutosh Bapat <ashutosh.bapat@enterprisedb.com> writes:
> On Wed, Nov 1, 2017 at 3:15 AM, Tom Lane <tgl@sss.pgh.pa.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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