WITH MRR_DIFF AS (
    SELECT 
        MIN(MONTHLY) AS MONTHLY
        , 0 AS MRR_DIFF
    FROM 
        MRR_DATA
    UNION
    SELECT 
        DATE(MONTHLY, "+1 MONTH") AS MONTHLY
        , NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR AS MRR_DIFF 
    FROM 
        MRR_DATA
)

SELECT 
    MONTHLY AS YM
    , SUM(MRR_DIFF) OVER(ORDER BY MONTHLY) AS MRR
FROM
    MRR_DIFF