Which SQL function to use to get previous month's data?

Question

Hi
The reporting need: Display of two month's payroll run results....current and previous (based on the parameter passed) in Oracle Discoverer.
Data source: A table in which run result values are stored. Of course to be linked to number of other tables.
Can somebody guide me on which SQL function to use to get the data for previous month?
Secondly, as Discoverer does not support parameters, I cannot put parameter in the query itself. I'll be applying parameter later while generating my report.
Please advice.
Thanks and regards,
Aparna

Answer 1

It's not very clear in my head... but you can try :
SQL> select * from test;
ENAM        SAL DT
TOTO       1000 30/05/06
TOTO       1001 20/04/06
TOTO       1002 11/03/06
TATA       2000 30/05/06
TATA       1500 20/04/06
TUTU       3500 30/05/06
6 rows selected.
SQL> select ename, dt, sal currmonth,
            case when trunc(lag(dt,1,dt) over (partition by ename order by dt),'MM') = trunc(add_months(dt,-1),'MM')
                 then lag(sal,1,sal) over (partition by ename order by dt)
                 else null end prevmonth
     from   test
SQL> /
ENAM DT        CURRMONTH  PREVMONTH
TATA 20/04/06       1500
TATA 30/05/06       2000       1500
TOTO 11/03/06       1002
TOTO 20/04/06       1001       1002
TOTO 30/05/06       1000       1001
TUTU 30/05/06       3500
6 rows selected.
SQL>
SQL> Nicolas.
Just an additional question : do the previous month is current month-1, or is there hole in month suite (e.g. the previous month can be current month-2) ?
Message was edited by:
N. Gasparotto