SQL - Average every n rows for items with same ID - sql

Question

I found a lot of similart posts, but any of them answered what I needed. Im trying to sumarize a big table (200M rows). What I need is to get the average every n (5 or something like that) for each ID. I've been trying with this:
select id, dev_id,
row_number() over(partition by dev_id order by dev_id) as rn,
avg(med1) over(order by dev_id rows between current row and 5 following) as avg_med1,
avg(med2) over(order by dev_id rows between current row and 5 following) as avg_med2
from my_table;
What I get with that query is a moving average, however, I only want the mean of the n elements for the current id. So the output should be for ID x > avg(rows 1-5), for ID x > avg(rows 6-10), for ID y > avg(rows 11-15)...
The thing im trying to replicate is something like the following:
From:
dev_id, med1, med2, med3
2, 3, 4, 1
3, 2, 1, 2
3, 1, 3, 9
3, 2, 4, 7
1, 3, 3, 2
2, 4, 3, 2
1, 5, 3, 2
3, 4, 2, 3
2, 4, 7, 2
To:
dev_id, AVG(med1), AVG(med2), AVG(med3)
2, 3.5, 3.5, 1.5
3, 1.5, 2, 5.5
3, 3, 3, 5
1, 4, 3, 2
2, 4, 5, 2

Answer 1

This ended up working for me, however is not what I initially planned it:
select id, reference, avg(b1), avg(b25), avg(b10), max(created_at)
from
(
select id,
#row_number := case when #reference = reference then #row_number + 1 else 0 end as row_number,
#reference := reference as reference,
b1,
b25,
b10,
created_at
from history_air
cross join (select #row_number := -1, #reference := '') as t
order by reference, created_at
) as t
group by reference, row_number div 150
order by reference, row_number div 150;