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From: Richard Guo <guofenglinux@gmail.com>
Date: Mon, 29 Jun 2026 09:39:20 +0900
Message-ID: 
 <CAMbWs4-6umOecRifmC88RW0SHWDAvb4c3-VD8XQ3NJufsUyUOQ@mail.gmail.com>
Subject: Re: BUG #19533: Wrong results from WindowAgg run-condition pushdown
 on count() with EXCLUDE CURRENT ROW
To: Chengpeng Yan <chengpeng_yan@outlook.com>
Cc: "imchifan@163.com" <imchifan@163.com>,
	"pgsql-bugs@lists.postgresql.org" <pgsql-bugs@lists.postgresql.org>,
 David Rowley <dgrowleyml@gmail.com>
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On Sun, Jun 28, 2026 at 1:53=E2=80=AFAM Chengpeng Yan <chengpeng_yan@outloo=
k.com> wrote:
> The attached patch takes the conservative route: int8inc_support() no
> longer reports count() as monotonic when the window frame has
> FRAMEOPTION_EXCLUSION. The added regression tests cover the reported
> case, related EXCLUDE variants, and a count(*) case. They also check
> that the excluded-frame query keeps a normal Filter instead of a
> WindowAgg Run Condition.

I think the fix is on the right track.  One nit is that it might be
better to use if/else if structure here.  The other nit is that the
test case is over-heavy; it should be kept as minimal as possible.

> Thoughts welcome on whether this is the right boundary, or whether some
> narrower excluded-frame cases should still prove monotonicity
> separately.

I wonder if we should still support count(*) with EXCLUDE CURRENT ROW,
as that always removes exactly one row, so it is still monotonic.

+   if ((frameOptions & FRAMEOPTION_EXCLUSION) &&
+       ((frameOptions & FRAMEOPTION_EXCLUSION) !=3D
FRAMEOPTION_EXCLUDE_CURRENT_ROW ||
+        req->window_func->winfnoid !=3D F_COUNT_))
+       monotonic =3D MONOTONICFUNC_NONE;

- Richard