SELECT
    MONTHLY AS YM,
    -- *,
    SUM(tmp_mrr) OVER(ORDER BY MONTHLY) AS MRR
FROM (        
    SELECT
        *,
        IFNULL(LAG(NEW_MRR) OVER(ORDER BY MONTHLY), 0) + IFNULL(LAG(EXPANSION_MRR) OVER(ORDER BY MONTHLY), 0) - IFNULL(LAG(DOWNGRADE_MRR) OVER(ORDER BY MONTHLY), 0) - IFNULL(LAG(CHURN_MRR) OVER(ORDER BY MONTHLY), 0) AS tmp_mrr
    FROM
        MRR_DATA
)
ORDER BY
    MONTHLY ASC