SQL> ed
Wrote file afiedt.buf

  1  with t (CODE,INNNP,SUMMA) as (
  2  select 1,10,100 from dual union all
  3  select 1,11,200 from dual union all
  4  select 1,12,300 from dual union all
  5  select 2,20,100 from dual
  6  )
  7  ,g as (
  8   select
  9      code,sum(summa) o
 10   from t
 11   group by code)
 12  SELECT
 13    t.CODE,SUMMA,o,decode(o,0,0,summa*100/o) "Доля %"
 14  from t,g
 15* where t.code=g.code
SQL> /

      CODE      SUMMA          O   Доля %
---------- ---------- ---------- --------
         1        100        600   16.667
         1        200        600   33.333
         1        300        600   50.000
         2        100        100  100.000