"add_months" and "interval"

Question

please tell me what is the difference between the below query.i need to take the last month date using the current date.Which query will be the correct one and whats the difference.
select trunc(sysdate)+ interval '1' month from dual;
select trunc(add_months(sysdate,1)) from dual;

Answer 1

1)select trunc(to_date('30-jan-2008','dd-mon-yyyy'))+ interval '1' month from dual;
2)select trunc(add_months(to_date('30-jan-2008','dd-mon-yyyy'),1)) from dual;you get to understand the difference from above examples....
in case of first query...if you add a interval 1 month then date is not valid because 30-feb-2008 doesn't exist...so the query will fail..
in case of second query...if you use add_months function...if there is no valid date next month...then it will take last day of the month like in above case...29-feb-2008.
so in your case depending upon your requirement you need to use 1 or 2...
Ravi Kumar
Edited by: ravikumar.sv on Aug 25, 2009 12:24 PM