oracle的connect by

--数形查询出所有的相关数据
select a.empno,a.ename,a.mgr,b.lv
from emp a
left join emp_level b on(b.empno=a.empno)
  start with a.empno=7876
connect by ((prior a.mgr)=a.empno
and (prior b.lv)>2);

也是看书的  prior b.lv >2 请大神求教?