STDDEV_POP 函数计算总体标准差。STDDEV_POP 函数将数值型数据作为参数，返回数值型数据。
注意
总体标准差是总体方差的算术平方根。
语法
STDDEV_POP([ALL] expr) [ OVER (analytic_clause) ]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
。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。
参数
参数 | 说明 |
|---|---|
ALL | 全部数值列。 |
OVER | 使用 |
expr | 是数值类型（ |
返回类型
返回类型与参数 expr 的数据类型相同。
示例
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, '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;调用函数并执行以下语句：
SELECT manager_id, last_name, salary, STDDEV_POP(salary) OVER (PARTITION BY manager_id) AS pop_std
FROM employees ORDER BY manager_id, last_name, salary, pop_std;查询结果如下：
+------------+-----------+--------+-------------------------------------------+
| MANAGER_ID | LAST_NAME | SALARY | POP_STD |
+------------+-----------+--------+-------------------------------------------+
| 100 | De Haan | 11000 | 5637.250548804798333699350384281939588505 |
| 100 | Errazuriz | 1400 | 5637.250548804798333699350384281939588505 |
| 100 | Hartstein | 14000 | 5637.250548804798333699350384281939588505 |
| 100 | Partners | 14000 | 5637.250548804798333699350384281939588505 |
| 100 | Raphaely | 1700 | 5637.250548804798333699350384281939588505 |
| 100 | Raphaely | 1700 | 5637.250548804798333699350384281939588505 |
| 100 | Russell | 13000 | 5637.250548804798333699350384281939588505 |
| 100 | Weiss | 13500 | 5637.250548804798333699350384281939588505 |
| 200 | Bell | 13000 | 408.248290463863016366214012450981899069 |
| 200 | Part | 14000 | 408.248290463863016366214012450981899069 |
| 200 | Ross | 13500 | 408.248290463863016366214012450981899069 |
+------------+-----------+--------+-------------------------------------------+聚合函数示例
调用函数并执行以下语句：
SELECT STDDEV_POP(salary) FROM employees ;查询结果如下：
+-------------------------------------------+
| STDDEV_POP(SALARY) |
+-------------------------------------------+
| 5249.950806538512715446505486136315088416 |
+-------------------------------------------+
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