select
    MONTHLY as YM,
    sum(g) over (
        order by
            monthly
    ) MRR
from
    (
        select
            x.monthly,
            ifnull(a.g, 0) g
        from
            (select monthly from mrr_data union all select DATE(max(monthly), '+1 months') from mrr_data) x
            left join (
                select
                    MONTHLY,
                    NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR as g
                from
                    MRR_DATA
            ) A on x.MONTHLY = DATE(A.MONTHLY, '+1 months')
        order by
            x.monthly
    ) a