INSERT INTO MRR_DATA VALUES ('2023-01-01', 0, 0, 0, 0);

WITH LAST_MONTH AS(
SELECT
    MONTHLY
    ,CASE 
        WHEN SUM(NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR) OVER(ORDER BY MONTHLY ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) IS NULL
        THEN 0
        ELSE SUM(NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR) OVER(ORDER BY MONTHLY ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING)
    END AS LM_SUM
FROM MRR_DATA
)

SELECT
    MONTHLY AS YM
    ,SUM(LM_SUM) OVER(ORDER BY MONTHLY ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS MMR
FROM LAST_MONTH