Horton

Re: Account for cost and selectivity of HAVING quals

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Tels <nospam-pg-abuse@bloodgate.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-10-31T23:54:08Z
Lists: pgsql-hackers 
On Tue, Oct 31, 2017 at 4:31 PM, Tels <nospam-pg-abuse@bloodgate.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.​

Commits

  1. Teach planner to account for HAVING quals in aggregation plan nodes.