with TMP as (
    select * from MRR_DATA
    union all
    select
        date(max(MONTHLY), '+1 month')
        , 0
        , 0
        , 0
        , 0
    from MRR_DATA
)
select
    YM
    , sum(TMP_MRR) over(order by YM rows between unbounded preceding and current row) as MRR
from (select
        MONTHLY as YM
        , coalesce(lag(NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR, 1)
            over(order by MONTHLY), 0) as TMP_MRR
    from TMP)
order by YM
;