with t1 as (
            select 1 id,5 s from dual union all
            select 2,15 from dual union all
            select 3,10 from dual union all
            select 4,50 from dual
           ),
      t2 as(
            select 1 id,10 s from dual union all
            select 2,25 from dual union all
            select 3,5 from dual
           )
select  nvl(t1.id,t2.id) id,
        nvl(t1.s,0) + nvl(t2.s,0) s
  from  t1 full join t2 on t2.id = t1.id
/
        ID          S
---------- ----------
         1         15
         2         40
         3         15
         4         50

SQL>