Regarding substracting dates

Question

Can we Substract 2 dates in the format 'WW-YYYY'
to get number of weeks??

Answer 1

Well your criteria aren't dates, they are just strings, so you need to extract the relevant parts and put those into the SQL... e.g.
SQL> ed
Wrote file afiedt.buf
  1  WITH mydates as (select '51-2008' as end_date, '24-2008' as start_date from dual)
  2  -- END OF TEST DATA
  3  select ((to_date('01-01-'||substr(end_date,4),'DD-MM-YYYY')+(to_number(substr(end_date,1,2))*7))
  4        - (to_date('01-01-'||substr(start_date,4),'DD-MM-YYYY')+(to_number(substr(start_date,1,2))*7))
  5         ) / 7 as weeks
  6* from mydates
SQL> /
     WEEKS
        27
SQL>