--
-- Тестовый набор данных 
-- (сорри за немного оракловый акцент, но он-лайн тестовую базу DB2 найти не смог):
with
  t11_dopl(reg, nd, np, kp, st, ns, sev) as 
    (
      select 6, 129241, date'1990-02-12', date'1991-10-14', '1-2', 0, 1 from dual union all
      select 6, 129241, date'1991-10-15', date'1995-09-30', '1-3', 0, 1 from dual union all
      select 6, 129241, date'1995-11-04', date'2001-12-31', '1-2', 0, 1 from dual union all
      select 6, 129241, date'2002-01-01', date'2009-12-31', '1-2', 0, 1 from dual
    )
--
-- Основной запрос (вроде все конструкции аналогичны "местному" синтаксису):
select reg, nd, min(np) as x_np, max(kp) as x_kp, st, ns, sev
  from (
         select reg, nd, st, ns, sev, np, kp, 
                sum(sog) over(partition by reg, nd, st, ns, sev
                                  order by np,kp) as grp_id
           from (
                  select reg, nd, st, ns, sev, np, kp, 
                         case 
                           when np <= max(kp + 1 day) over(partition by reg, nd, st, ns, sev
                                                           order by np, kp 
                                                            rows between unbounded preceding
                                                             and 1 preceding) 
                             then 0 
                           else 1 
                         end as sog -- sog = start_of_group :)
                    from t11_dopl
                )
       )
 group by reg, nd, st, ns, sev, grp_id
 order by reg, nd, st, ns, sev, x_np