rollup   配合   goup   by   命令使用，可以提供信息汇总功能（类似于"小计"）
文章出处：http://www.diybl.com/course/7_databases/oracle/oraclejs/2008224/101034.html

SQL>   select   job,deptno,sal   from   emp;  
   
  JOB                     DEPTNO               SAL  
  ---------   ---------   ---------  
  CLERK                         20               800  
  SALESMAN                   30             1600  
  SALESMAN                   30             1250  
  MANAGER                     20             2975  
  SALESMAN                   30             1250  
  MANAGER                     30             2850  
  MANAGER                     10             2450  
  ANALYST                     20             3000  
  PRESIDENT                 10             5000  
  SALESMAN                   30             1500  
  CLERK                         20             1100  
  CLERK                         30               950  
  ANALYST                     20             3000  
  CLERK                         10             1300  
   
  已选择14行。  
   
  SQL>   select   job,deptno,sum(sal)   total_sal   from   emp   group   by   rollup(job,deptno);  
   
  JOB                     DEPTNO   TOTAL_SAL  
  ---------   ---------   ---------  
  ANALYST                     20             6000  
  ANALYST                                     6000  
  CLERK                         10             1300  
  CLERK                         20             1900  
  CLERK                         30               950  
  CLERK                                         4150  
  MANAGER                     10             2450  
  MANAGER                     20             2975  
  MANAGER                     30             2850  
  MANAGER                                     8275  
  PRESIDENT                 10             5000  
  PRESIDENT                                 5000  
  SALESMAN                   30             5600  
  SALESMAN                                   5600  
                                                  29025  
   
  已选择15行。  
   
  SQL> 

SELECT
 CASE WHEN A.JOB IS NULL AND A.DEPTNO IS NULL THEN '汇总'
         WHEN A.JOB IS NOT NULL AND  A.DEPTNO IS NULL THEN A.JOB ||  '小计'
 ELSE A.JOB END JOB,
 CASE WHEN  A.DEPTNO IS NULL THEN '/' ELSE TO_CHAR(A.DEPTNO) END DEPTNO,
 SUM(A.SAL) TOTAL_SAL
  FROM EMP A
 WHERE A.JOB IS NOT NULL
 GROUP BY ROLLUP(JOB, DEPTNO);

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