with a as
 (select 'За полученный товар по Договору N 555/12 от 29.04.11 Сумма 999999-00В т.ч. НДС(18%) 179999-82' str1
    from dual),
b as
 (select 'За полученный товар по Договору N 444/13 от 30.05.12 Сумма 1111-55В т.ч. НДС(18%) 200-08' str2
    from dual),
a_sym as
 (select level a_n, substr(a.str1, level, 1) a_s
    from a
  connect by level <= length(a.str1)),
b_sym as
 (select level b_n, substr(b.str2, level, 1) b_s
    from b
  connect by level <= length(b.str2)),
ab_com as
 (select a_s ab
    from a_sym
  intersect
  select b_sym.b_s from b_sym)
select listagg(a_s, '') within group (order by a_n)
  from a_sym
 where a_sym.a_s in (select ab from ab_com)
 order by a_sym.a_n

with a as
 (select 'За полученный товар по Договору N 555/12 от 29.04.11 Сумма 999999-00В т.ч. НДС(18%) 179999-82' str1
    from dual),
b as
 (select 'За полученный товар по Договору N 444/13 от 30.05.12 Сумма 1111-55В т.ч. НДС(18%) 200-08' str2
    from dual),
a_sym as
 (select level a_n, substr(a.str1, level, 1) a_s
    from a
  connect by level <= length(a.str1)),
b_sym as
 (select level b_n, substr(b.str2, level, 1) b_s
    from b
  connect by level <= length(b.str2)),
ab_com as
 (select a_s ab
    from a_sym
  intersect
  select b_sym.b_s from b_sym)
select listagg(b_s, '') within group (order by b_n)
  from b_sym
 where b_sym.b_s in (select ab from ab_com)
 order by b_sym.b_n