STDDEV_SAMP

声明

STDDEV_SAMP(expr)

说明

返回 expr 的样本标准差，该函数返回 VAR_SAMP() 函数结果的平方根。有关 VAR_SAMP() 函数的详细信息，请参见 VAR_SAMP。

如果没有匹配到行，则该函数返回 NULL。

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 STDDEV_SAMP(salary) FROM employees;
+---------------------+
| STDDEV_SAMP(salary) |
+---------------------+
|   5506.194858355616 |
+---------------------+
1 row in set (0.001 sec)