Inserting the incorrect Year - 0009 instead of 2009

Question

I have a data entry screen on which I have two date columns. Initiation date is system date and Due date which I select from the calendar java script. Depending on the values of these two fields, I calculate the target date by multiply some percentage with the number of week days between the two dates. The value in these two dates is correct all the time
My problem is sometime the year of date is correct and sometimes the year is incorrect. e.g. 0009 instead of 2009. The code is
var_date := to_date(p_init_date,'dd-mon-yy') + numdays2;
Do you think the next code will make the difference
var_date := to_date(p_init_date,'DD-MON-RRRR') + numdays2;
Why it works most of the times and does not work once in a while? Has anybody have this problem?
Thanks
Yagna

Answer 1

Hi, Yagna,
That's an excellent question.
Do some experiments, like the query below, and find out for yourself:
ALTER SESSION     SET NLS_DATE_FORMAT = 'DD-Mon-YYYY';
WITH  test_data  AS
     SELECT  '01-Jan-09'     AS txt FROM dual  UNION ALL
     SELECT  '03-Feb-009'    AS txt FROM dual  UNION ALL
     SELECT  '04-Feb-0009'   AS txt FROM dual  UNION ALL
--     add more test cases here, if you want.  Copy and modify the line above.
     SELECT     '24-Apr-2009'   AS txt FROM dual
SELECT     txt
,     TO_DATE (txt, 'DD-Mon-YY')     AS yy
,     TO_DATE (txt, 'DD-Mon-RRRR')     AS rrrr
,     TO_DATE (txt, 'DD-Mon-RR')     AS rr
FROM     test_data;TO_DATE tries very hard not to raise an error. For example, if the first argument has a 4-digit year, but the second argument says the year will only have 2-digits, TO_DATE will act as if the 2-nd argument has a 4-digit year, too.