WITH LAST_YEAR_MRR_DATA AS (
    SELECT
        MONTHLY,
        (lag(NEW_MRR, 1) over (order by MONTHLY)) + (lag(EXPANSION_MRR, 1) over (order by MONTHLY)) - (lag(DOWNGRADE_MRR, 1) over (order by MONTHLY)) - (lag(CHURN_MRR, 1) over (order by MONTHLY)) AS LAST_YEAR_MRR
    FROM
        MRR_DATA
)

SELECT
    m.MONTHLY AS YM,
    ifNull(lm.LAST_YEAR_MRR, 0) AS MRR
FROM
    MRR_DATA m
INNER JOIN
    LAST_YEAR_MRR_DATA lm
    ON m.MONTHLY = lm.MONTHLY
ORDER BY
    YM
;