1  with t as (
  2  select 'c1' c, 1 s from dual union all
  3  select 'c2' c, 2 s from dual union all
  4  select 'c3' c, 10 s from dual union all
  5  select 'c4' c, -5 s from dual union all
  6  select 'c5' c, 20 s from dual)
  7  select sum(s)
  8  ,sum(decode(c,'c3',s)) c3
  9  ,sum(decode(c,'c4',s)) c4
 10  ,case when sum(decode(c,'c3',s))> sum(decode(c,'c4',s)) then sum(s)
 11  else sum(decode(c,'c3',0,'c4',0,s)) end ss
 12* from t
SQL> /

    SUM(S)         C3         C4         SS
---------- ---------- ---------- ----------
        28         10         -5         28