SQL> with t as
  2  (
  3      select 1 type_, 1 f1, 2 f2 from dual union all
  4      select 2 type_, 0 f1, 10 f2 from dual union all
  5      select null type_, -1 f1, -2 f2 from dual
  6  )
  7  select
  8      type_,
  9      decode(type_, 1, f1, 2, f2, -1000) f
 10  from
 11      t
 12  /

     TYPE_          F
---------- ----------
         1          1
         2         10
                -1000