Baseline calculation

Question

Hi all ,
I have a table that holds data about dates ..
Table :
MonthYear
2011/12
2011/01
2010/08
I need to get the baseline of each row as below
Baseline
2011/06
2010/07
2010/02
ie Baseline=Monthyear - 6 months
Create table mon(monthyear date);
I am using Oracle 11g
select monthyear-6 as baseline from mon;
I used the above query but I think days are getting subtracted .
Please Help
Regards,
Sana .

Answer 1

Hi, Sana,
If monthyear is a DATE, then just use ADD_MONTHS:
SELECT     monthyear
,     ADD_MONTHS (monthyear, -6)
FROM     table_x
;Information about dates belongs in a DATE column, even if you're only interested in the year and month.
If monthyear is a VARCHAR2, then use TO_DATE to create a DATE from it, and then use TO_CHAR to convert it back, if necessary:
SELECT     monthyear
,     TO_CHAR ( ADD_MONTHS ( TO_DATE (monthyear, 'YYYY/MM')
                      , -6
          , 'YYYY/MM'
          )          AS baseline
FROM     table_x
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only), and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Always say which version of Oracle you're using.
Edited by: Frank Kulash on Feb 24, 2012 10:03 AM