WITH TMP AS(
SELECT 
    MONTHLY
    ,NEW_MRR
    ,EXPANSION_MRR
    ,DOWNGRADE_MRR
    ,CHURN_MRR
    ,LAG(NEW_MRR,1) 
        OVER(ORDER BY MONTHLY ASC) AS FR_NM
    ,LAG(EXPANSION_MRR,1) 
        OVER(ORDER BY MONTHLY ASC) AS FR_EM
    ,LAG(DOWNGRADE_MRR,1) 
        OVER(ORDER BY MONTHLY ASC) AS FR_DM
    ,LAG(CHURN_MRR,1) 
        OVER(ORDER BY MONTHLY ASC) AS FR_CM
FROM
    MRR_DATA
)
,TMP2 AS(
SELECT
    MONTHLY
    ,FR_NM+ FR_EM - FR_DM - FR_CM AS MRR
FROM
    TMP
)

SELECT
    MONTHLY
    ,CASE WHEN (SUM(MRR) OVER(ORDER BY MONTHLY ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)) IS NOT NULL THEN (SUM(MRR) OVER(ORDER BY MONTHLY ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)) ELSE 0 END  AS MRR
FROM
    TMP2