GROUP BY GROUPING SETS((),
通过grouping sets 设置多个分组，网上看到的一个例子：

SQL> SELECT CASE
  2           WHEN a.deptno IS NULL THEN
  3            '合计'
  4           WHEN a.deptno IS NOT NULL AND a.empno IS NULL THEN
  5            '小计'
  6           ELSE
  7            '' || a.deptno
  8         END deptno,
  9         a.empno,
10         a.ename,
11         SUM(a.sal) total_sal
12    FROM scott.emp a
13  GROUP BY GROUPING SETS((a.deptno),(a.deptno, a.empno, a.ename),());

DEPTNO                                   EMPNO ENAME       TOTAL_SAL
---------------------------------------- ----- ---------- ----------
10                                        7782 CLARK            2450
10                                        7839 KING             5000
10                                        7934 MILLER           1300
小计                                                            8750
20                                        7369 SMITH             800
20                                        7566 JONES            2975
20                                        7788 SCOTT            3000
20                                        7