複数注文の場合の償却額の計算方法について

CREATE TABLE #t 
( id INT ,
dingdan VARCHAR(20),
sale MONEY
) 

INSERT INTO #t VALUES (1,'a',100);
INSERT INTO #t VALUES (2,'b',200);  
INSERT INTO #t VALUES (3,'c',300);  
INSERT INTO #t VALUES (4,'d',400);  
INSERT INTO #t VALUES (5,'e',500);  
INSERT INTO #t VALUES (6,'f',600);  
INSERT INTO #t VALUES (7,'g',700);
INSERT INTO #t VALUES (8,'h',800);
INSERT INTO #t VALUES (9,'i',900);
INSERT INTO #t VALUES (10,'j',1000);

;WITH x1
     AS ( SELECT t1.id ,
            t1.dingdan ,
            t1.sale ,
            ( SELECT ISNULL(SUM(t2.sale), 0)
             FROM #t t2
             WHERE t2.id < t1.id
            ) AS curr_sale_sum - the amount of all orders prior to this order
        FROM #t t1
       ),/* Calculate the write-off amount*/
    x2
     AS ( SELECT id ,
            dingdan ,
            sale ,
            CASE WHEN curr_sale_sum + sale <= 1700 THEN sale
               ELSE 1700 - curr_sale_sum
            END AS new_sale
        FROM x1
       )
   /* If the write-off amount is negative, change it to 0*/
  SELECT id AS serial number,
      dingdan order,
      sale order amount,
      CASE WHEN new_sale < 0 THEN 0
         ELSE new_sale
      END AS write off amount
  FROM x2