| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | ma lz <ma100(at)hotmail(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Why not do distinct before SetOp |
| Date: | 2024-11-05 23:38:00 |
| Message-ID: | CAApHDvrXUuhGJ_rzsuLY3f1mou1w5RT4zxEb45gbBR3ap6vy4g@mail.gmail.com |
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| Lists: | pgsql-general |
On Wed, 6 Nov 2024 at 12:09, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Of course, I might be overestimating the performance benefit we'd get.
> But I'm tempted to give it a try.
I'm glad. I'm curious to see if you're right about the projection
overhead of the flags. If you're right, it seems like a not too
difficult optimisation to get in.
I like the idea as it also gets rid of the flag cruft from
prepunion.c, which saves having to add flags conditionally if
INTERCEPT/EXCEPT were ever made to use joins.
David
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