Hi,
just another way using rownum:
scott@oracle> select rownum rn, empno, ename from emp;



        RN      EMPNO ENAME

---------- ---------- ----------

         1       7369 SMITH

         2       7499 ALLEN

         3       7521 WARD

         4       7566 JONES

         5       7654 MARTIN

         6       7698 BLAKE

         7       7782 CLARK

         8       7788 SCOTT

         9       7839 KING

        10       7844 TURNER

        11       7876 ADAMS

        12       7900 JAMES

        13       7902 FORD

        14       7934 MILLER



14 rows selected.



scott@oracle> select rn, empno, ename from

  2  ( select empno, ename, rownum rn from emp )

  3  where mod(rn,2)=1;



        RN      EMPNO ENAME

---------- ---------- ----------

         1       7369 SMITH

         3       7521 WARD

         5       7654 MARTIN

         7       7782 CLARK

         9       7839 KING

        11       7876 ADAMS

        13       7902 FORD



7 rows selected.

Ales