Proverei a spostare parte dei calcoli nella fase di inserimento riga.
Aggiungi una nuova colonna:
alter table measurements add consumption real;
Aggiorna la colonna:
with m1 as (
select
id, power_total, created_at,
lag(power_total) over (partition by device_id order by created_at) prev_power_total,
lag(created_at) over (partition by device_id order by created_at) prev_created_at
from measurements
)
update measurements m2
set consumption =
(m1.power_total+ m1.prev_power_total)*
extract(epoch from m1.created_at- m1.prev_created_at)
from m1
where m2.id = m1.id;
Crea un attivatore:
create or replace function before_insert_on_measurements()
returns trigger language plpgsql
as $$
declare
rec record;
begin
select power_total, created_at into rec
from measurements
where device_id = new.device_id
order by created_at desc
limit 1;
new.consumption:=
(new.power_total+ rec.power_total)*
extract(epoch from new.created_at- rec.created_at);
return new;
end $$;
create trigger before_insert_on_measurements
before insert on measurements
for each row execute procedure before_insert_on_measurements();
La domanda:
select device_id, sum(consumption) total_consumption
from measurements
-- where conditions
group by 1
order by 1
