15일차 # 7-10: Level, a Hierarchical Query Pseudocolumn

   select level, e.* from emp e;

--> ORA-01788: CONNECT BY clause required in this query block

select level, e.*

from emp e

start with empno =  7839    

connect by prior empno = mgr;

    -- 원하는 레벨만 확인하기

select level, e.* 

from emp e

where level in (1, 2)

start with empno =  7839    

connect by prior empno = mgr;