WITH premonth AS(
    SELECT
        NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR 
    FROM
        MRR_DATA
    WHERE
        MONTHLY = YM
)
, indextbl AS(
    SELECT
        (SELECT min(MONTHLY) FROM MRR_DATA) as YM
        , 0 AS MRR
    UNION ALL
    select
        DATE(YM, '+1 month')
        , MRR + (SELECT * FROM premonth)
    FROM
        indextbl
    where
        YM < DATE ((SELECT max(MONTHLY) FROM MRR_DATA), '1 month')
)
select * from indextbl order by YM ASC;