GROUPING SETS与GROUP_ID

SELECT E.DEPARTMENT_ID DID,
       E.JOB_ID JOB,
       E.MANAGER_ID MID,
       SUM(E.SALARY) SUM_SAL,
       COUNT(E.EMPLOYEE_ID) CNT,
       GROUP_ID() GG
  FROM EMPLOYEES E
 WHERE E.JOB_ID IN ('ST_CLERK', 'SH_CLERK', 'MK_REP', 'MK_MAN')
 GROUP BY GROUPING SETS((E.DEPARTMENT_ID, E.JOB_ID), E.MANAGER_ID, E.JOB_ID)
 ORDER BY E.DEPARTMENT_ID, E.JOB_ID, E.MANAGER_ID;
  DID JOB        MID    SUM_SAL        CNT         GG
----- ---------- ------- ---------- ---------- ----------
   20 MK_MAN                  13000          1          0
   20 MK_REP                   6000           1           0
   50 SH_CLERK                64300         20          0
   50 ST_CLERK                55700         20          0
        MK_MAN                  13000          1          0
        MK_REP                   6000           1           0
        SH_CLERK                64300         20          0
        ST_CLERK                55700         20          0
                     100            13000          1          0
                     120            22100          8          0
                     121           25400           8          0
                     122           23600           8          0
                     123           25900           8          0
                     124           23000           8          0
                     201           6000             1          0