| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | "Finnerty, Jim" <jfinnert(at)amazon(dot)com> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Removing useless DISTINCT clauses |
| Date: | 2018-08-23 22:38:47 |
| Message-ID: | CAKJS1f83wb3WYHsnqFnv-BXXKDSAJ2SDVXTEWDXRffV2LaoeyA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 24 August 2018 at 03:29, Finnerty, Jim <jfinnert(at)amazon(dot)com> wrote:
> Thank you Álvaro. Here's the distinct_opt_v7 patch.
Determining if there's just 1 base relation by checking the length the
rtable is not a good way. If you want to see why, try creating a
primary key on a partitioned table.
My personal opinion of only being able to completely remove the
DISTINCT when there's a single item in the rtable (or a single base
table) is that it's just too poor to bother with. I think such a
solution is best left to another patch and it should be much more
complete and be able to track the unique properties through joins.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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