SQL> create table t ( a int, b int, c int, d int );

Table created.

SQL>
SQL> insert into t values (1,2,3,4);

1 row created.

SQL>
SQL> select
  2    a,
  3    b,
  4    c,
  5    a+b-c+d/2+10-sqrt(c) as ugh
  6  from t;

         A          B          C        UGH
---------- ---------- ---------- ----------
         1          2          3 10.2679492

1 row selected.

SQL>
SQL> select
  2    a,
  3    b,
  4    c,
  5    ugh,
  6    case when ugh > 0 then 'Y' else 'N' end more_stuff
  7  from
  8    (
  9        select
 10          a,
 11          b,
 12          c,
 13          a+b-c+d/2+10-sqrt(c) as ugh
 14  from t
 15  );

         A          B          C        UGH M
---------- ---------- ---------- ---------- -
         1          2          3 10.2679492 Y

1 row selected.