with S as (
    select
        ifnull(L.MONTHLY,(select date(max(MONTHLY), '+1 months') from MRR_DATA)) as YM,
        ifnull(R.NEW_MRR + R.EXPANSION_MRR - R.DOWNGRADE_MRR - R.CHURN_MRR, 0) as MMR
    from
        MRR_DATA L
    full outer join
        MRR_DATA R
    on
        date(L.MONTHLY, '-1 months') = R.MONTHLY
)



select
    YM,
    sum(MMR) over (order by YM) as MRR
from
    S
order by
    YM asc