1  with t as (
  2  select TO_CHAR(add_months(to_date(t.date_from,'dd.mm.yyyy'),0), 'FMMONTH', 'NLS_DATE_LANGUAGE = RUSSIAN') as mmm
  3  ,date_from
  4  from (
  5   select decode(level,1,d1,trunc(add_months(d1,level-1),'mm')) as date_from
  6   from (
  7   select to_date('01.01.2017','dd.mm.yyyy') d1,
  8   to_date('01.08.2017','dd.mm.yyyy') d2
  9   from dual
 10   )
 11   connect by add_months(trunc(d1,'mm'),level-1) <= d2
 12  )t
 13  )
 14* select listagg(mmm,'; ') within group(order by date_from) s  from t
SQL> /

S
--------------------------------------------------------------------------------
ЯНВАРЬ; ФЕВРАЛЬ; МАРТ; АПРЕЛЬ; МАЙ; ИЮНЬ; ИЮЛЬ; АВГУСТ

select * from (
    select TO_CHAR(add_months(to_date(t.date_from,'dd.mm.yyyy'),0), 'MONTH', 'NLS_DATE_LANGUAGE = RUSSIAN') as mmm
    from (
    select decode(level,1,d1,trunc(add_months(d1,level-1),'mm')) as date_from
    from (
    select to_date('01.01.2017','dd.mm.yyyy') d1,
    to_date('01.08.2017','dd.mm.yyyy') d2
    from dual
    )
    connect by add_months(trunc(d1,'mm'),level-1) <= d2
    ) t
)
pivot (max(mmm) for mmm in ('ЯНВАРЬ' month1, 'ФЕВРАЛЬ' month2))