"partition by" giving incorrect value - postgresql

Question

battery_pct tstamp charging phone_id
90 t1 yes 12
91 t2 yes 22
95 t3 no 22
89 t4 no 22
87 t5 no 22
80 t6 no 22
78 t7 yes 22
85 t8 yes 4
50 t9 no 4
40 t10 no 4
38 t11 no 4
20 t12 yes 4
I want to calculate battery depletion rate as : change in battery / time taken
This should be calculated for ALL the windows when charging is 'no' (sandwiched in between 2 "yes"), and then the average of those rates should be taken.
So, for this dataset it should be:
95 - 80 / t6 - t3 = rate for phone_id 22
50 - 38 / t11 - t9 = rate for phone_id 4
average rate = ( rate 1 + rate 2 ) / 2
Please note there can be more than one windows of no's for each phone_id in the data.
I have to find average rate across ALL phone id's. i.e. one value for average rate which encompasses all phones.
Here is my current code, it does not give any error, but is returning a value that is NOT plausible -
with discharge_intervals as (
select battery_pct, tstamp,
sum((charging = 'yes')::int) over (partition by phone_id order by tstamp) as ival_number,
charging = 'no' as keep
from dataset
), interval_rates as (
select ival_number,
(max(battery_pct) - min(battery_pct))
/ extract(epoch from max(tstamp) - min(tstamp)) as ival_rate
from discharge_intervals
where keep
group by ival_number
)
select avg(ival_rate)
from interval_rates;

Answer 1

Your interval_rates are calculated without grouping by phone, but should be. The ival_numbers are partitioned by phone_id, but that just means multiple phones will create rows with the same ival_number. You'll want to use
with discharge_intervals as (
select battery_pct, tstamp, phone_id,
-- ^^^^^^^^^
sum((charging = 'yes')::int) over (partition by phone_id order by tstamp) as ival_number,
charging = 'no' as keep
from dataset
), interval_rates as (
select (max(battery_pct) - min(battery_pct))
/ extract(epoch from max(tstamp) - min(tstamp)) as ival_rate
from discharge_intervals
where keep
group by phone_id, ival_number
-- ^^^^^^^^^
)
select avg(ival_rate)
from interval_rates;