Selecting multiple columns conditionally in Oracle10g
SELECT column1,
       column2,
       column3,
       column4,
       column5,
       column6,
   --If this condition is not met the following columns are not selected
   IF password = password
   (
       conditional_column1,
       conditional_column2,
       conditional_column3
   )
FROM source_table
WHERE username = username

SQL> create or replace procedure dyn_emp( p_include_empno in boolean,
  2                                       p_rc           out sys_refcursor )
  3  as
  4    l_sql varchar2(1000);
  5  begin
  6    l_sql := 'SELECT ename ';
  7    if( p_include_empno )
  8    then
  9      l_sql := l_sql || ', empno ';
 10    end if;
 11    l_sql := l_sql || ' from emp';
 12    open p_rc for l_sql;
 13  end;
 14  /

Procedure created.

SQL> variable rc refcursor;
SQL> exec dyn_emp( true, :rc );

PL/SQL procedure successfully completed.

SQL> print rc

ENAME           EMPNO
---------- ----------
SMITH            7369
ALLEN            7499
WARD             7521
JONES            7566
MARTIN           7654
BLAKE            7698
CLARK            7782
SCOTT            7788
KING             7839
TURNER           7844
ADAMS            7876
JAMES            7900
FORD             7902
MILLER           7934

14 rows selected.

SQL> exec dyn_emp( false, :rc );

PL/SQL procedure successfully completed.

SQL> print rc

ENAME
----------
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS
JAMES
FORD
MILLER

14 rows selected.