Group By Grouping Sets

Group by分組函數的自定義，與group by配合使用可更加靈活的對結果集進行分組，Grouping sets會對各個層級進行彙總，而後將各個層級的彙總值union all在一塊兒，但卻比單純的group by + union all 效率要高

 

1 建立數據

CREATE TABLE employee
(
  name          NVARCHAR2(10),
  gender        NCHAR(1),
  country       NVARCHAR2(10),
  department    NVARCHAR2(10),
  salary        NUMBER(10)
);
INSERT INTO employee VALUES ('張三','男','中國','市場部',4000);
INSERT INTO employee VALUES ('李四','男','中國','市場部',5000);
INSERT INTO employee VALUES ('王五','女','美國','市場部',3000);  
INSERT INTO employee VALUES ('趙紅','男','中國','技術部',2000);
INSERT INTO employee VALUES ('李白','女','中國','技術部',5000);  
INSERT INTO employee VALUES ('王藍','男','美國','技術部',4000);
commit;

 

2 實例

SELECT country, null department, round(avg(salary), 2) FROM employee GROUP BY country
UNION ALL
SELECT null country, department, round(avg(salary), 2) FROM employee GROUP BY department;
等價於
SELECT country, department, round(avg(salary), 2) FROM employee GROUP BY GROUPING SETS (country, department);


GROUP BY GROUPING SETS (A,B,C)  等價與  GROUP BY A  
                                        UNION ALL  
                                        GROUP BY B  
                                        UNION ALL  
                                        GROUP BY C
                                        
                                        
GROUP BY GROUPING SETS ((A,B,C))  等價與  GROUP BY A,B,C  
   
   
GROUP BY GROUPING SETS (A,(B,C))  等價與  GROUP BY A  
                                          UNION ALL  
                                          GROUP BY B,C

                                        
GROUP BY GROUPING SETS (A)  等價於  GROUP BY A,B,C  
        ,GROUPING SETS (B)  
        ,GROUPING SETS (C)  
   
   
GROUP BY GROUPING SETS (A)  等價於  GROUP BY A,B,C  
        ,GROUPING SETS ((B,C))   
   
   
GROUP BY GROUPING SETS (A)  等價於  GROUP BY A,B  
        ,GROUPING SETS (B,C)        UNION ALL  
                                    GROUP BY A,C
                                    
                                    
GROUP BY A                     等價於  GROUP BY A  
        ,B                                     ,B  
        ,GROUPING SETS ((B,C))                 ,C  
   
   
GROUP BY A                    等價於  GROUP BY A,B,C  
        ,B                            UNION ALL  
        ,GROUPING SETS (B,C)          GROUP BY A,B  
   
   
GROUP BY A                    等價於 GROUP BY A,B,C  
        ,B                           UNION ALL  
        ,C                           GROUP BY A,B,C  
        ,GROUPING SETS (B,C)