WITH basis AS
(SELECT MONTH(release_date) months, SUM(sale_amt) tot_amt
   FROM box_office
  WHERE YEAR(release_date) = 2019
  GROUP BY 1
),
finals AS
(SELECT months, tot_amt,
        LAG(tot_amt) OVER (ORDER BY months) pre_month_amt
   FROM basis
)
SELECT months, tot_amt,
       ROUND((tot_amt - pre_month_amt) / pre_month_amt * 100, 2) rates
  FROM finals
 ORDER BY 1;