Oracle学习:start with connect by prior

一、案例

select empno, mgr, level as lv
from scott.emp a
start with mgr is null
connect by prior empno = mgr
order by level;

--start with:表示起始行为哪个
--connect by prior empno = mgr:表示当前列的某个字段(这里是起始行mgr为空的empn