SQL> create or replace
  2    function f1
  3      return sys.OdciVarchar2List
  4      pipelined
  5      is
  6      begin
  7          for v_rec in (select ename from emp where deptno = 10) loop
  8            pipe row(v_rec.ename);
  9          end loop;
 10  end;
 11  /

Function created.

SQL> create or replace
  2    function f2
  3      return sys.OdciVarchar2List
  4      pipelined
  5      is
  6      begin
  7          for v_rec in (select ename from emp where deptno = 20) loop
  8            pipe row(v_rec.ename);
  9          end loop;
 10  end;
 11  /

Function created.

SQL> create or replace
  2    function f3
  3      return sys.OdciVarchar2List
  4      pipelined
  5      is
  6      begin
  7          for v_rec in (select ename from emp where deptno = 30) loop
  8            pipe row(v_rec.ename);
  9          end loop;
 10  end;
 11  /

Function created.

SQL> create or replace
  2    function f(
  3               p_deptno number
  4              )
  5      return sys.OdciVarchar2List
  6      pipelined
  7      is
  8      begin
  9          if p_deptno = 10
 10            then
 11              for v_rec in (select column_value from table(f1)) loop
 12                pipe row(v_rec.column_value);
 13              end loop;
 14          elsif p_deptno = 20
 15            then
 16              for v_rec in (select column_value from table(f2)) loop
 17                pipe row(v_rec.column_value);
 18              end loop;
 19          elsif p_deptno = 30
 20            then
 21              for v_rec in (select column_value from table(f3)) loop
 22                pipe row(v_rec.column_value);
 23              end loop;
 24            else
 25              raise_application_error(-20500,'invalid deptno');
 26          end if;
 27  end;
 28  /

Function created.

SQL> select  *
  2    from  f(20)
  3  /

COLUMN_VALUE
--------------------------------------------------------------------------------------
SMITH
JONES
SCOTT
ADAMS
FORD

SQL> select  *
  2    from  f(10)
  3  /

COLUMN_VALUE
--------------------------------------------------------------------------------------
CLARK
KING
MILLER

SQL>