SELECT
    YM
  , SUM(mrr_buf) OVER(ORDER BY YM) - mrr_buf as MRR
FROM
   (SELECT
        MONTHLY AS YM
      , NEW_MRR + EXPANSION_MRR - DOWNGRADE_MRR - CHURN_MRR AS mrr_buf
    FROM MRR_DATA
    /*「年月が最も新しいレコードの翌月」行を追加する */
    UNION
    SELECT
        DATE(MAX(MONTHLY), "+1 MONTH") AS YM
      , 0 AS mrr_buf
    FROM MRR_DATA
   ) MRR_DATA2
ORDER BY
    YM