GROUPING
声明
GROUPING(expr)
说明
GROUP BY 可以通过 WITH ROLLUP 子句将各分组进行汇总以表示更高级的聚合（也称为超聚合），并产生额外的行。例如以下 SQL 可以将销售额按年度分组，并输出各分组的汇总。
其中 year 为 NULL 的行即超聚合行。
SELECT year, SUM(profit) AS profit
FROM sales
GROUP BY year WITH ROLLUP;
+------+--------+
| year | profit |
+------+--------+
| 2000 | 4525 |
| 2001 | 3010 |
| NULL | 7535 |
+------+--------+
WITH ROLLUP 修饰多个 GROUP BY 列时，结果会更加复杂。在这种情况下，每一个分组都会产生一个超聚合行。例如以下 SQL 会产生额外的超聚合行。
SELECT year, country, product, SUM(profit) AS profit
FROM sales
GROUP BY year, country, product WITH ROLLUP;
+------+---------+------------+--------+
| year | country | product | profit |
+------+---------+------------+--------+
| 2000 | Finland | Computer | 1500 |
| 2000 | Finland | Phone | 100 |
| 2000 | Finland | NULL | 1600 |
| 2000 | India | Calculator | 150 |
| 2000 | India | Computer | 1200 |
| 2000 | India | NULL | 1350 |
| 2000 | USA | Calculator | 75 |
| 2000 | USA | Computer | 1500 |
| 2000 | USA | NULL | 1575 |
| 2000 | NULL | NULL | 4525 |
| 2001 | Finland | Phone | 10 |
| 2001 | Finland | NULL | 10 |
| 2001 | USA | Calculator | 50 |
| 2001 | USA | Computer | 2700 |
| 2001 | USA | TV | 250 |
| 2001 | USA | NULL | 3000 |
| 2001 | NULL | NULL | 3010 |
| NULL | NULL | NULL | 7535 |
+------+---------+------------+--------+
GROUPING 函数用于对超聚合行进行区分，如果返回的行是超聚合行，则该函数返回 1，否则返回 0。
例如对上述 SQL 进行改写，利用 GROUPING 函数的特性添加判断。
SELECT
IF(GROUPING(year), 'All years', year) AS year,
IF(GROUPING(country), 'All countries', country) AS country,
IF(GROUPING(product), 'All products', product) AS product,
SUM(profit) AS profit
FROM sales
GROUP BY year, country, product WITH ROLLUP;
+-----------+---------------+--------------+--------+
| year | country | product | profit |
+-----------+---------------+--------------+--------+
| 2000 | Finland | Computer | 1500 |
| 2000 | Finland | Phone | 100 |
| 2000 | Finland | All products | 1600 |
| 2000 | India | Calculator | 150 |
| 2000 | India | Computer | 1200 |
| 2000 | India | All products | 1350 |
| 2000 | USA | Calculator | 75 |
| 2000 | USA | Computer | 1500 |
| 2000 | USA | All products | 1575 |
| 2000 | All countries | All products | 4525 |
| 2001 | Finland | Phone | 10 |
| 2001 | Finland | All products | 10 |
| 2001 | USA | Calculator | 50 |
| 2001 | USA | Computer | 2700 |
| 2001 | USA | TV | 250 |
| 2001 | USA | All products | 3000 |
| 2001 | All countries | All products | 3010 |
| All years | All countries | All products | 7535 |
+-----------+---------------+--------------+--------+
示例
CREATE TABLE employees (manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(100, 'De Haan', '2018-05-01',11000);
INSERT INTO employees VALUES(100, 'Errazuriz', '2017-07-21', 1400);
INSERT INTO employees VALUES(100, 'Hartstein', '2019-05-01',14000);
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-22', 1700);
INSERT INTO employees VALUES(100, 'Weiss', '2019-07-11',13500);
INSERT INTO employees VALUES(100, 'Russell', '2019-10-05', 13000);
INSERT INTO employees VALUES(100, 'Partners', '2018-12-01',14000);
INSERT INTO employees VALUES(200, 'Ross', '2019-06-11',13500);
INSERT INTO employees VALUES(200, 'Bell', '2019-05-25', 13000);
INSERT INTO employees VALUES(200, 'Part', '2018-08-11',14000);
COMMIT;
SELECT IF(GROUPING(manager_id),'manager_id',manager_id) AS manager_id,SUM(SALARY) FROM employees GROUP BY manager_id WITH ROLLUP;
+------------+-------------+
| manager_id | SUM(SALARY) |
+------------+-------------+
| 100 | 70300 |
| 200 | 40500 |
| manager_id | 110800 |
+------------+-------------+
3 rows in set (0.001 sec)