Connected to:
Oracle9i Enterprise Edition Release  9 . 2 . 0 . 7 . 0  - 64bit Production
With the Partitioning option
JServer Release  9 . 2 . 0 . 7 . 0  - Production

SQL> define ColumnList = "rownum VAL1, dummy VAL2"
SQL> select &ColumnList from dual;
old    1 : select &ColumnList from dual
new    1 : select rownum VAL1, dummy VAL2 from dual

      VAL1 V
---------- -
          1  X

SQL> select & 1  from dual;
Enter value for  1 :  123  as Z
old    1 : select & 1  from dual
new    1 : select  123  as Z from dual

         Z
----------
        123 

SQL>

select &ColumnList &ColumnList2 from dual;

Connected to:
Oracle9i Enterprise Edition Release  9 . 2 . 0 . 7 . 0  - 64bit Production
With the Partitioning option
JServer Release  9 . 2 . 0 . 7 . 0  - Production

SQL> define StaticColumnList = "rownum VAL1, dummy VAL2"
SQL> define VarColumnList = ''
SQL> column VarColumnList new_value VarColumnList noprint
SQL> select decode(& 1 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual;
Enter value for  1 :  100 
old    1 : select decode(& 1 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual
new    1 : select decode( 100 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual




SQL> select &StaticColumnList &VarColumnList from dual;
old    1 : select &StaticColumnList &VarColumnList from dual
new    1 : select rownum VAL1, dummy VAL2  from dual

      VAL1 V
---------- -
          1  X

SQL> select decode(& 2 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual;
Enter value for  2 :  1 
old    1 : select decode(& 2 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual
new    1 : select decode( 1 ,'1',', rownum*10-100 VAR1','') VarColumnList from dual




SQL> select &StaticColumnList &VarColumnList from dual;
old    1 : select &StaticColumnList &VarColumnList from dual
new    1 : select rownum VAL1, dummy VAL2 , rownum* 10 - 100  VAR1 from dual

      VAL1 V       VAR1
---------- - ----------
          1  X        - 90 

SQL>