Re: Aggregate leads to superfluous projection from the scan

On Fri, Jul 8, 2022 at 9:40 AM Zhihong Yu <zyu(at)yugabyte(dot)com> wrote:

> Hi,
> Here is the query which involves aggregate on a single column:
>
>
> https://dbfiddle.uk/?rdbms=postgres_13&fiddle=44bfd8f6b6b5aad34d00d449c04c5a96
>
> As you can see from `Output:`, there are many columns added which are not
> needed by the query executor.
>
> I wonder if someone has noticed this in the past.
> If so, what was the discussion around this topic ?
>
> Thanks
>
Hi,
With the patch, I was able to get the following output:

explain (analyze, verbose) /*+ IndexScan(t) */select count(fire_year) from
fires t where objectid <= 2000000;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=119.00..119.01 rows=1 width=8) (actual time=9.453..9.453
rows=1 loops=1)
Output: count(fire_year)
-> Index Scan using fires_pkey on public.fires t (cost=0.00..116.50
rows=1000 width=4) (actual time=9.432..9.432 rows=0 loops=1)
Output: fire_year
Index Cond: (t.objectid <= 2000000)
Planning Time: 52.598 ms
Execution Time: 13.082 ms

Please pay attention to the column list after `Output:`

Tom:
Can you take a look and let me know what I may have missed ?

Thanks