Someone

SELECT COUNT(DISTINCT(cust_cod)) , no_of_mon , v2.total AS total FROM churn CROSS JOIN ( SELECT SUM(cnt) as total FROM ( SELECT COUNT(DISTINCT(cust_cod)) as cnt FROM churn WHERE sales_reg = '80' AND pack_cod = 'UTH0021' GROUP BY no_of_mon) AS v1) AS v2 WHERE sales_reg = '80' AND pack_cod = 'UTH0021' GROUP BY no_of_mon, v2.total;
 count | no_of_mon | total
-------+-----------+-------
     2 |         6 |  1579
     9 |         7 |  1579
    11 |         8 |  1579
    12 |         9 |  1579
    17 |        10 |  1579
    31 |        11 |  1579
    44 |        12 |  1579
  1162 |        13 |  1579
   291 |        14 |  1579

i need to substract the total with the count for sucessive rows

eg


 count | no_of_mon | total
-------+-----------+-------
     2 |         6 |  1579
     9 |         7 |  1577
    11 |         8 |  1569
    12 |         9 |  1558
    17 |        10 |  1546
    31 |        11 |  1511
    44 |        12 |  .
  1162 |        13 |  .
   291 |        14 |  .
etc