How to write the following SELECT

Question

CARDS     Commission
0-20     0
21-25     500
26-31     650
32-36     850
37>     1050
If an PERSON sells 28 cards in a month, commission would be computed as below.
25*500 = 12500
3*650 = 1950
Total commission 14450

Answer 1

New solution:
SQL > var cards_sold       NUMBER;
SQL > exec :cards_sold := 28;
PL/SQL procedure successfully completed.
SQL >
SQL > WITH COMM_TABLE AS
  2  (
  3     SELECT 0 AS MIN_CARD, 20 AS MAX_CARD, 0 AS COMMISSION FROM DUAL UNION ALL
  4     SELECT 21 AS MIN_CARD, 25 AS MAX_CARD, 500 AS COMMISSION FROM DUAL UNION ALL
  5     SELECT 26 AS MIN_CARD, 31 AS MAX_CARD, 650 AS COMMISSION FROM DUAL UNION ALL
  6     SELECT 32 AS MIN_CARD, 36 AS MAX_CARD, 850 AS COMMISSION FROM DUAL UNION ALL
  7     SELECT 37 AS MIN_CARD, NULL AS MAX_CARD, 1000 AS COMMISSION FROM DUAL
  8  )
  9  SELECT     LEAD(PART_COMMISSION,1) OVER (ORDER BY MAX_CARD DESC)
10             +       (:cards_sold-LEAD(MAX_CARD,1) OVER (ORDER BY MAX_CARD DESC))*COMMISSION  AS COMMISSION
11  FROM
12  (
13     SELECT  COMM_TABLE.*
14     ,       COMM_TABLE.COMMISSION*COMM_TABLE.MAX_CARD AS PART_COMMISSION
15     FROM    COMM_TABLE
16     WHERE   MIN_CARD <= :cards_sold
17     ORDER BY MIN_CARD DESC
18  )
19  WHERE ROWNUM <= 2;
COMMISSION
     14450Explanation:
/* According to your requirements commission is calculated in two parts.
* The first part is equal to the COMMISSION value for the RANGE that the :cards_sold exceeds (21-25 in this case)
* multiplied by the MAX_CARDs value in that range. This is indicated by (A) below.
* The second part is the COMMISSION in the range that the :cards_sold is included in multipled by the
* difference of the :cards_sold and the MAX_CARD values for the RANGE that the :cards_sold exceeds (21-25 in this case).
* This is indicated by (B) below.
SELECT      LEAD(PART_COMMISSION,1) OVER (ORDER BY MAX_CARD DESC) /* (A) */
          +     (:cards_sold-LEAD(MAX_CARD,1) OVER (ORDER BY MAX_CARD DESC))*COMMISSION /* (B) */ AS COMMISSION
FROM
     SELECT      COMM_TABLE.*
     ,     COMM_TABLE.COMMISSION*COMM_TABLE.MAX_CARD AS PART_COMMISSION /* (A) */     
     FROM     COMM_TABLE
     WHERE     MIN_CARD <= :cards_sold     /* We are only interested in the entries where the # of cards sold is greater than the minimum */
     ORDER BY MIN_CARD DESC
WHERE ROWNUM <= 2; /* Only need one commission value */