Oracle date function for the previous month

Question

I have the query below where the date is hard-coded. My objective is to remove the harcoded date; the query should pull the data for the previous month when it runs.

select count(distinct switch_id)
  from [email protected]
 where dealer_name =  'XXXX'
   and TRUNC(CREATION_DATE) BETWEEN '01-AUG-2012' AND '31-AUG-2012'

Should I use sysdate-15 function for that?

Answer 1

Modifying Ben's query little bit,

 select count(distinct switch_id)   
  from [email protected]  
 where dealer_name =  'XXXX'    
   and creation_date between add_months(trunc(sysdate,'mm'),-1) and last_day(add_months(trunc(sysdate,'mm'),-1))