宣言
GROUPING(expr)
説明
GROUP BY は WITH ROLLUP 句を使用して各グループを集計し、より高次の集計（スーパー集計とも呼ばれる）を表現するとともに、追加の行を生成できます。例えば、以下のSQLは売上高を年度ごとにグループ化し、各グループの集計値を出力します。
ここで、year が NULL の行はスーパー集計行です。
obclient> SELECT year, SUM(profit) AS profit
FROM sales
GROUP BY year WITH ROLLUP;
+------+--------+
| year | profit |
+------+--------+
| 2000 | 4525 |
| 2001 | 3010 |
| NULL | 7535 |
+------+--------+
WITH ROLLUP が複数の GROUP BY 列を修飾する場合、結果はさらに複雑になります。この場合、各グループに対してスーパー集計行が生成されます。例えば、以下のSQLは追加のスーパー集計行を生成します。
obclient> 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 関数はスーパー集計行を区別するために使用されます。返される行がスーパー集計行の場合、この関数は 1 を返し、そうでない場合は 0 を返します。
例えば、上記のSQLを書き直し、GROUPING関数の特性を活用して判断を追加します。
obclient> 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 |
+-----------+---------------+--------------+--------+
例
obclient> 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;
obclient> 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