Sample Code in SQL: generate cumulative numbers by day

for simplicity the sample table x only has two columns: day_key and number

create temp table x3 as
select x.day_key as day_key, x.number as number, x2.day_key as cum_day,x2.number as cum_number
from x
join (select * from x) x2
on x.day_key>=x2.day_key
;

select day_key, sum(cum_number)
from x3
where x3.day_key>=x3.cum_day
group by 1;