sql>select level, empno, ename, job, mgr
  2    from emp
  3   start with mgr is null
  4   connect by prior empno = mgr;
 
    LEVEL     EMPNO ENAME      JOB             MGR
--------- --------- ---------- --------- ---------
        1      7839 KING       PRESIDENT
        2      7566 JONES      MANAGER        7839
        3      7788 SCOTT      ANALYST        7566
        4      7876 ADAMS      CLERK          7788
        3      7902 FORD       ANALYST        7566
        4      7369 SMITH      CLERK          7902
        2      7698 BLAKE      MANAGER        7839
        3      7499 ALLEN      SALESMAN       7698
        3      7521 WARD       SALESMAN       7698
        3      7654 MARTIN     SALESMAN       7698
        3      7844 TURNER     SALESMAN       7698
        3      7900 JAMES      CLERK          7698
        2      7782 CLARK      MANAGER        7839
        3      7934 MILLER     CLERK          7782
 
14 rows selected.