WITH mrr_calc AS (
  SELECT
    MONTHLY,
    NEW_MRR,
    EXPANSION_MRR,
    DOWNGRADE_MRR,
    CHURN_MRR,
    COALESCE(
      LAG(NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR) OVER (ORDER BY MONTHLY),
      0
    ) as PREVIOUS_MRR
  FROM
    MRR_DATA
)
SELECT
  MONTHLY AS YM,
  NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR + PREVIOUS_MRR as MRR
FROM
  mrr_calc
ORDER BY
  YM ASC;