Re: BUG #17495: Regression in 15beta1 when filtering subquery including row_number window function

On Thu, May 26, 2022 at 1:38 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:

> On Thu, 26 May 2022 at 16:34, Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> > On Thu, May 26, 2022 at 12:13 PM Richard Guo <guofenglinux(at)gmail(dot)com>
> wrote:
> >>
> >>
> >> On Thu, May 26, 2022 at 11:47 AM David Rowley <dgrowleyml(at)gmail(dot)com>
> wrote:
> >>>
> >>> The problem is that the qual pushdown stuff all happens in
> >>> set_subquery_pathlist() before we call subquery_planner() for the
> >>> subquery. We don't yet have a PlannerInfo made for the subquery when
> >>> we call check_and_push_window_quals(). We don't really have any other
> >>> means to communicate to subquery_planner() what the run conditions are
> >>> for the given Query object. Plus, we *do* really need to know what the
> >>> runConditions are before we call subquery_planner() so that those
> >>> conditions can be properly tagged onto WindowAggPaths. I don't really
> >>> think it would be right to pluck those from the PlannerInfo when we
> >>> later call create_plan(). That wouldn't leave us any opportunity to do
> >>> any costing related stuff with run conditions if we decide to do that
> >>> later.
> >>
> >>
> >> The remove_unused_subquery_outputs() also happens before we call
> >> subquery_planner() for the subquery. Cann't we just store the attnos
> >> used in window quals that are pushed down to runConditions in the
> >> PlannerInfo of the upper query?
> >
> >
> > Ah, your point is to move runConditions also out of WindowClause and
> > store them in PlannerInfo, right? That's indeed not an easy job.
>
> Yeah, I was aiming for a way to have it so the planner didn't
> vandalise WindowClause.
>
> I've attached a patch which fixes the bug and does not require any
> further modifications to WindowClause.
>

The patch looks sane to me, expect that line 122 in the patch introduces
a whitespace-only line.

BTW, surprised that param 'attno' in find_window_run_conditions() is not
used before.

So after this fix, do we plan to further move runConditions out of
WindowClause so that we don't need to modify the input parse tree?

Thanks
Richard