WITH tbl AS (
    SELECT
        A.MONTHLY
        , B.NEW_MRR
        , B.EXPANSION_MRR
        , B.DOWNGRADE_MRR
        , B.CHURN_MRR
        
    FROM MRR_DATA AS A 
        LEFT OUTER JOIN MRR_DATA AS B
        ON A.MONTHLY = DATE(B.MONTHLY, '1 month')
        
    ORDER BY 1
    
), tbl2 AS (
    SELECT
        MONTHLY
        , IFNULL(NEW_MRR,0) + IFNULL(EXPANSION_MRR, 0)
            - IFNULL(DOWNGRADE_MRR, 0) - IFNULL(CHURN_MRR, 0) AS MRR
    FROM tbl
)

SELECT 
    tbl.MONTHLY AS YM
    , tbl2.MRR
        + IFNULL(tbl.NEW_MRR,0) + IFNULL(tbl.EXPANSION_MRR, 0)
        - IFNULL(tbl.DOWNGRADE_MRR, 0) - IFNULL(tbl.CHURN_MRR, 0) AS MRR
    
FROM tbl INNER JOIN tbl2 USING(MONTHLY)
ORDER BY 1