Calculating given occurance of a given day in every month

Question

Hi,
I'm using oracle 10.2.0.1.0 and forms 6i.
I have inputs like frequency, day and start date.
Suppose
Start Date : 12-03-2011
Day : Saturday
Frequency : 2
What i want to do is, i want to calculate 2nd occurance of saturday(2nd Saturday), in every month, starting from the given date, till the end of the year.
The given start date, is anyway the 2nd occurance of saturday in March.
So now in april -- its is 09-04-2011
May -- 14-05-2011
June -- 11-06-2011
Is there a way to calculate like this?
Please help
Thanks

Answer 1

Hi,
Another way is to use the NEXT_DAY function, like this:
WITH     parameters     AS
     SELECT     DATE '2011-03-12'     AS start_date
     ,     'SATURDAY'          AS week_day
     ,     2               AS week_num     -- This isn't really a frequency
     FROM     dual
,     all_dates     AS
     SELECT  start_date
     ,     NEXT_DAY ( ADD_MONTHS ( TRUNC (start_date, 'MONTH')
                          , LEVEL - 1
                          ) + (7 * week_num)
                         - 8
                 , week_day
                )     AS a_date
     FROM     parameters
     CONNECT BY     LEVEL     <= 12
SELECT       a_date
FROM       all_dates
WHERE       a_date          >= start_date
AND       TRUNC (a_date, 'YEAR') = TRUNC (start_date, 'YEAR')
ORDER BY  a_date
;If you're doing this in Oracle Forms, then you don't need a sub-query like parameters. You can pass the parameters in PL/SQL variables, and use dual as the base table in all_dates (or use a PL/SQL loop).
The calculation of a_date works like this:
First, we find the beginning of the month.
Then, we add wekk_num weeks to that. For example, if week_num=2, that will give us the beginning of the 3rd week.
We're interested in the week before that, so we subtract 7, and we also subtract another 1 because NEXT_DAY always returns a date after (not the same as) its 1st argument.
Unfortunately, NEXT_DAY is always dependent on NLS_LANGUAGE. If you specify 'Saturday', but that day is called 'Lördag' in your NLS language, you'll get an error. If that's a possibility, then you can change the first sub-query like this:
WITH     parameters     AS
     SELECT     DATE '2011-03-12'     AS start_date
     ,     TO_CHAR ( DATE '2011-04-02'     -- or any Saturday
               , 'DAY'          
               )          AS week_day
     ,     2               AS week_num
     FROM     dual
) ...Instead of April 2, 2011, you can you any Saturday you want; just be sure it's a Saturday.