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

not really in direct response to this conversation, but is there any reason

on the face of the planet why read receipts need to be sent to every single

recipient of the mailing list?

just saying,

  richard

---- On Fri, 28 Jun 2024 03:20:26 -0400 <agharta82(at)gmail(dot)com> wrote ---

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 mailto:agharta82(at)gmail(dot)com,
<mailto: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