Re: Todo: Teach planner to evaluate multiple windows in the optimal order

> On 08/01/23 21:36, Vik Fearing wrote:

> On 1/8/23 11:21, Ankit Kumar Pandey wrote:
>> 
>> Please find attached patch with addressed issues mentioned before.


> I am curious about this plan:

> +-- ORDER BY's in multiple Window functions can be combined into one
> +-- if they are subset of QUERY's ORDER BY
> +EXPLAIN (COSTS OFF)
> +SELECT empno,
> +       depname,
> +       min(salary) OVER (PARTITION BY depname ORDER BY empno) depminsalary,
> +       sum(salary) OVER (PARTITION BY depname) depsalary,
> +       count(*) OVER (ORDER BY enroll_date DESC) c
> +FROM empsalary
> +ORDER BY depname, empno, enroll_date;
> +                      QUERY PLAN
> +------------------------------------------------------
> + WindowAgg
> +   ->  WindowAgg
> +         ->  Sort
> +               Sort Key: depname, empno, enroll_date
> +               ->  WindowAgg
> +                     ->  Sort
> +                           Sort Key: enroll_date DESC
> +                           ->  Seq Scan on empsalary
> +(8 rows)
> +


> Why aren't min() and sum() calculated on the same WindowAgg run?

Isn't that exactly what is happening here? First count() with sort on 
enroll_date is run and

then min() and sum()?


Only difference between this and plan generated by master(given below) 
is a sort in the end.

                          QUERY PLAN
------------------------------------------------------------
  Incremental Sort
    Sort Key: depname, empno, enroll_date
    Presorted Key: depname, empno
    ->  WindowAgg
          ->  WindowAgg
                ->  Sort
                      Sort Key: depname, empno
                      ->  WindowAgg
                            ->  Sort
                                  Sort Key: enroll_date DESC
                                  ->  Seq Scan on empsalary

Let me know if I am missing anything. Thanks.

-- 
Regards,
Ankit Kumar Pandey