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