Re: A way to optimize sql about the last temporary-related row

HOO-HA! This is HUGE!

Only 2.2 seconds on my data!!!! Amazing!

distinct on (field) *followed by "*" *is a hidden gem!

Thank you so much and thanks to everyone who helped me!  Thank you very
much!!

Cheers,

Agharta

Il 27/06/24 6:16 PM, David Rowley ha scritto:
>
>
> On Fri, 28 Jun 2024, 3:20 am agharta82(at)gmail(dot)com,
> <agharta82(at)gmail(dot)com> wrote:
>
>
> Now the query:
> explain (verbose, buffers, analyze)
> with last_table_ids as materialized(
>    select xx from (
>    select LAST_VALUE(pk_id) over (partition by integer_field_2
> order by
> datetime_field_1 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED
> FOLLOWING) xx
>    from test_table
>    where integer_field_1 = 1
>    and datetime_field_1 <= CURRENT_TIMESTAMP
>    ) ww group by ww.xx
>
> ),
> last_row_per_ids as (
>    select tt.* from last_table_ids lt
>    inner join test_table tt on (tt.pk_id = lt.xx)
>
> )
>
> select * /* or count(*) */ from last_row_per_ids;
>
>
> This query, on my PC, takes 46 seconds!!!
>
>
> (Away from laptop and using my phone)
>
> Something like:
>
> select distinct on (integer_field_2) * from test_table where
> integer_field_1 = 1 and datetime_field_1 <= CURRENT_TIMESTAMP order by
> integer_field_2,datetime_field_1 desc;
>
> Might run a bit faster.  However if it's slow due to I/O then maybe
> not much faster.  Your version took about 5 seconds on my phone and my
> version ran in 1.5 seconds.
>
> It's difficult for me to check the results match with each query from
> my phone. A quick scan of the first 10 or so records looked good.
>
> If the updated query is still too slow on cold cache then faster disks
> might be needed.
>
> David
>