| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Tels <nospam-pg-abuse(at)bloodgate(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Account for cost and selectivity of HAVING quals |
| Date: | 2017-10-31 23:54:08 |
| Message-ID: | CAKFQuwb=ZKj1RnJBt4fn1xhBdRJGPJfsHEs0HYrNgD9zgvU35g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Oct 31, 2017 at 4:31 PM, Tels <nospam-pg-abuse(at)bloodgate(dot)com> wrote:
>
>
> That looks odd to me, it first uses output_tuples in a formula, then
> overwrites the value with a new value. Should these lines be swapped?
>
IIUC it is correct: the additional total_cost comes from processing every
output group to check whether it is qualified - since every group is
checked the incoming output_tuples from the prior grouping is used. The
side-effect of the effort is that the number of output_tuples has now been
reduced to only those matching the qual - and so it now must take on a new
value to represent this.
David J.
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