Re: Removing unneeded self joins

On Thu, May 27, 2021 at 12:21 PM Andrey V. Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
>
> On 5/8/21 2:00 AM, Hywel Carver wrote:
> > On Fri, May 7, 2021 at 8:23 AM Andrey Lepikhov
> > <a(dot)lepikhov(at)postgrespro(dot)ru <mailto:a(dot)lepikhov(at)postgrespro(dot)ru>> wrote:
> > Here I didn't work on 'unnecessary IS NOT NULL filter'.
> >
> > I've tested the new patch, and it is giving the same improved behaviour
> > as the old patch.
> Thank you for this efforts!
>
> I cleaned the code of previous version, improved regression tests and
> rebased on current master.
>
> Also, I see that we could do additional optimizations for an
> EC-generated selfjoin clause (See equivclass.patch for necessary
> changes). Example:
> explain (costs off)
> select * from sj t1, sj t2 where t1.a = t1.b and t1.b = t2.b and t2.b =
> t2.a;
> QUERY PLAN
> -----------------------------------------------------
> Seq Scan on sj t2
> Filter: ((a IS NOT NULL) AND (b = a) AND (a = b))
> (2 rows)
>
> But I'm not sure that this patch need to be a part of the self-join
> removal feature because of code complexity.

The patch does not apply on Head anymore, could you rebase and post a
patch. I'm changing the status to "Waiting for Author".

Regards,
Vignesh