select extract(month from v.ddate_from),
             extract(year from v.ddate_from),
             extract(month from v.ddate_to),
             extract(year from v.ddate_to)
        into dmonth1, dyear1, dmonth2, dyear2
        from T1 v
       where v.NPRN = r.nrn;

select sum(vpd.nsumm)
          into dbo
          from T2 vpd
         where vpd.nprn = user_num
           and vpd.nyear between dyear1 and dyear2
           and vpd.nmonth between dmonth1 and dmonth2;