with t1 as (
select 'window' as window, charge_at::date, sum(gross_amount) as rev from public.monthly_charges
where charge_at >= current_date - 30
  and charge_at < current_date
group by 1,2
order by 2 desc

), t2 as (
select
  *,
  avg(rev) over (partition by window) as avg_rev
from t1
)

select * from t2