select
    X.MONTHLY as YM
    ,sum(conMRR) over(order by X.MONTHLY range between UNBOUNDED PRECEDING and 1 PRECEDING) as MRR
from (
        select MONTHLY, NEW_MRR, EXPANSION_MRR, DOWNGRADE_MRR, CHURN_MRR
            ,(NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR) as conMRR
        from MRR_DATA
        union all
        select 
            date(min(MONTHLY), '-1 months') as MONTHLY
            ,0 as NEW_MRR
            ,0 as EXPANSION_MRR
            ,0 as DOWNGRADE_MRR
            ,0 as CHURN_MRR
            ,0 as conMRR
        from MRR_DATA
) X
order by X.MONTHLY