作为分析函数使用时,您需要使用窗口函数的完整语法,它对一组行的集合进行计算并返回多个值,具体信息请查阅文档 OVER (analytic_clause) 。作为聚合函数使用时,该函数对一组行的集合进行聚合计算,结果只能返回一个值,此时不需要加 OVER
关键字。
返回类型与参数 expr
的数据类型相同。
分析函数示例
以下语句创建了表 employees,并向里面插入数据:
CREATE TABLE employees (manager_id INT, last_name varchar(50), hiredate varchar(50), SALARY INT);
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(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;
返回结果如下:
+------------+-----------+------------+--------+------------------------------------------+
| MANAGER_ID | LAST_NAME | HIREDATE | SALARY | C_MAVG |
+------------+-----------+------------+--------+------------------------------------------+
| 100 | Raphaely | 2017-07-22 | 1700 | 4700 |
| 100 | De Haan | 2018-05-01 | 11000 | 8900 |
| 100 | Partners | 2018-12-01 | 14000 | 13000 |
| 100 | Weiss | 2019-07-11 | 13500 | 13500 |
| 100 | Russell | 2019-10-05 | 13000 | 13250 |
| 200 | Part | 2018-08-11 | 14000 | 13500 |
| 200 | Bell | 2019-05-25 | 13000 | 13500 |
| 200 | Ross | 2019-06-11 | 13500 | 13250 |
+------------+-----------+------------+--------+------------------------------------------+
聚合函数示例
执行以下语句计算 salary 的平均值:
+------------------------------------------+
| AVG(SALARY) |
+------------------------------------------+
| 10072.7272727272727272727272727272727273 |