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From: Andy Fan <zhihui.fan1213@gmail.com>
Date: Wed, 18 Aug 2021 20:20:45 +0800
Message-ID: 
 <CAKU4AWq5MB_inrYUwPQYXU1fCopCwgYK53N2uYGYFBH3QEhZMA@mail.gmail.com>
Subject: Re: Window Function "Run Conditions"
To: David Rowley <dgrowleyml@gmail.com>
Cc: Zhihong Yu <zyu@yugabyte.com>,
	PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
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Hi David:

Thanks for the patch.

On Wed, Aug 18, 2021 at 6:40 PM David Rowley <dgrowleyml@gmail.com> wrote:
>
> On Tue, 17 Aug 2021 at 03:51, Zhihong Yu <zyu@yugabyte.com> wrote:
> > +               if ((res->monotonic & MONOTONICFUNC_INCREASING) =3D=3D =
MONOTONICFUNC_INCREASING)
> >
> > The above can be simplified as 'if (res->monotonic & MONOTONICFUNC_INCR=
EASING) '
>
> True.  I've attached an updated patch.
>
> David

Looks like we need to narrow down the situation where we can apply
this optimization.

SELECT * FROM
  (SELECT empno,
          salary,
                  count(*) over (order by empno desc) as c      ,
          dense_rank() OVER (ORDER BY salary DESC) dr

   FROM empsalary) emp
WHERE dr =3D 1;

In the current master, the result is:

 empno | salary | c | dr

-------+--------+---+----

     8 |   6000 | 4 |  1

(1 row)

In the patched version=EF=BC=8C the result is:

 empno | salary | c | dr

-------+--------+---+----

     8 |   6000 | 1 |  1

(1 row)

--=20
Best Regards
Andy Fan (https://www.aliyun.com/)