② CONNECT_BY_ROOT

CONNECT_BY_ROOT는 계층형 쿼리에서 최상위 로우를 반환하는 연산자다. 연산자이므로 CONNECT_BY_ROOT 다음에는 표현식이 온다.

입력

    SELECT department_id, LPAD(' ' , 3 * (LEVEL-1)) || department_name, LEVEL,
           CONNECT_BY_ROOT department_name AS root_name
      FROM departments
     START WITH parent_id IS NULL
    CONNECT BY PRIOR department_id  = parent_id;