Generate due dates

Question

create table bills (id int,next_dt date,frequency varchar2(1));
insert into bills values (1,to_date('6/15/2013','mm/dd/yyyy'),'M'); -- Monthly
insert into bills values (2,to_date('6/15/2013','mm/dd/yyyy'),'W'); -- Weekly
insert into bills values (3,to_date('6/15/2013','mm/dd/yyyy'),'S'); -- Semi-annual
Given this data, how would one write a query to generate "due dates" for each item based on its frequency i.e. For id=1, the next payment date would be 7/15/2013 (1 month after the date specified), for id=2, it would be 6/22/2013 (1 week after its current date) and for id=3, it would be 12/15/2013 (6 months after its current date). Each row should generate the same number of "future" dates, say 6.
Help? Thanks

Answer 1

Hi,
Here's one way:
WITH cntr AS
        SELECT  LEVEL AS n
        FROM    dual
        CONNECT BY LEVEL <= 6     -- number of due dates to show
SELECT   b.id, b.next_dt, b.frequency
,       CASE  b.frequency
            WHEN  'W'  THEN  b.next_dt + (c.n * 7)
            WHEN  'M'  THEN  ADD_MONTHS (b.next_dt, c.n)
            WHEN  'S'  THEN  ADD_MONTHS (b.next_dt, c.n * 6)
        END AS due_dt
FROM        bills b
CROSS JOIN  cntr c
ORDER BY  b.id
,         c.n
Output:
        ID NEXT_DT     F DUE_DT
         1 15-Jun-2013 M 15-Jul-2013
         1 15-Jun-2013 M 15-Aug-2013
         1 15-Jun-2013 M 15-Sep-2013
         1 15-Jun-2013 M 15-Oct-2013
         1 15-Jun-2013 M 15-Nov-2013
         1 15-Jun-2013 M 15-Dec-2013
         2 15-Jun-2013 W 22-Jun-2013
         2 15-Jun-2013 W 29-Jun-2013
         2 15-Jun-2013 W 06-Jul-2013
         2 15-Jun-2013 W 13-Jul-2013
         2 15-Jun-2013 W 20-Jul-2013
         2 15-Jun-2013 W 27-Jul-2013
         3 15-Jun-2013 S 15-Dec-2013
         3 15-Jun-2013 S 15-Jun-2014
         3 15-Jun-2013 S 15-Dec-2014
         3 15-Jun-2013 S 15-Jun-2015
         3 15-Jun-2013 S 15-Dec-2015
         3 15-Jun-2013 S 15-Jun-2016