层次查询

SQL> --层次查询
SQL> select level,empno,ename,mgr
  2  from emp
  3  connect by prior empno=mgr
  4  start with mgr is null
  5  order by 1;

     LEVEL      EMPNO ENAME             MGR                                                                                                                                                             
---------- ---------- ---------- ----------                                                                                                                                                             
         1       7839 KING                                                                                                                                                                              
         2       7566 JONES            7839                                                                                                                                                             
         2       7698 BLAKE            7839                                                                                                                                                             
         2       7782 CLARK            7839                                                                                                                                                             
         3       7902 FORD             7566                                                                                                                                                             
         3       7521 WARD             7698                                                                                                                                                             
         3       7900 JAMES            7698                                                                                                                                                             
         3       7934 MILLER           7782                                                                                                                                                             
         3       7499 ALLEN            7698                                                                                                                                                             
         3       7788 SCOTT            7566                                                                                                                                                             
         3       7654 MARTIN           7698                                                                                                                                                             

     LEVEL      EMPNO ENAME             MGR                                                                                                                                                             
---------- ---------- ---------- ----------                                                                                                                                                             
         3       7844 TURNER           7698                                                                                                                                                             
         4       7876 ADAMS            7788                                                                                                                                                             
         4       7369 SMITH            7902                                                                                                                                                             

已选择 14 行。