oracle 中 group by 加强

group by rollup(a,b)
 =
 group by a,b
 +
 group by a
 +
 group by null

 SQL> select deptno,job,sum(sal)
   2  from emp
   3   group by rollup(deptno,job);

 DEPTNO JOB         SUM(SAL)
 ------ --------- ----------
                        2000
                        2000
     10 CLERK           1400
     10 MANAGER         2450
     10 PRESIDENT       5000
     10                 8850
     20 CLERK            800
     20 ANALYST         3000
     20 MANAGER         2975
     20                 6775
     30 CLERK            950
     30 MANAGER         2850
     30 SALESMAN        5600
     30                 9400
                       27025

 15 rows selected