STDDEV_SAMP

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功能描述

计算累积样本标准差(样本方差的平方根)。

语法格式

STDDEV_SAMP([ DISTINCT | ALL ]expr) [ OVER (analytic_clause) ]

输入参数

• expr：输入数据，DOUBLE类型。
• analytic_clause：可选的分析子句，支持分组子句，排序子句以及范围子句，详情见analytic_clause。

输出结果

输出结果为DOUBLE类型，当输入只有一行时或输入参数为NULL，返回NULL。

示例

-- 创建示例表
SQL> CREATE TABLE employees
     (
         empno    NUMBER(4) CONSTRAINT pk_emp PRIMARY KEY,
         ename    VARCHAR2(10),
         job      VARCHAR2(9),
         mgr      NUMBER(4),
         hiredate DATE,
         sal      NUMBER(7,2),
         comm     NUMBER(7,2),
         deptno   NUMBER(2)
     );

-- 插入数据
SQL> INSERT INTO employees VALUES
    (7369, 'SMITH', 'CLERK', 7902, TO_DATE('17-12-1980', 'DD-MM-YYYY'), 800, NULL, 20),
    (7499, 'ALLEN', 'SALESMAN', 7698, TO_DATE('20-2-1981', 'DD-MM-YYYY'), 1600, 300, 30),
    (7521, 'WARD', 'SALESMAN', 7698, TO_DATE('22-2-1981', 'DD-MM-YYYY'), 1250, 500, 30),
    (7566, 'JONES', 'MANAGER', 7839, TO_DATE('2-4-1981', 'DD-MM-YYYY'), 2975, NULL, 20),
    (7654, 'MARTIN', 'SALESMAN', 7698, TO_DATE('28-9-1981', 'DD-MM-YYYY'), 1250, 1400, 30),
    (7698, 'BLAKE', 'MANAGER', 7839, TO_DATE('1-5-1981', 'DD-MM-YYYY'), 2850, NULL, 30),
    (7934, 'MILLER', 'CLERK', 7782, TO_DATE('23-1-1982', 'DD-MM-YYYY'), 1300, NULL, 10);

SQL> SELECT STDDEV_SAMP(sal) "STDDEV_SAMP" FROM employees;

+--------------------------+
|       STDDEV_SAMP        |
+--------------------------+
| 849.59724351628883476122 |
+--------------------------+

SQL> SELECT ename, sal, STDDEV_SAMP(sal) OVER (ORDER BY hiredate) "STDDEV_SAMP" FROM employees WHERE deptno = 30 ORDER BY ename, sal, "STDDEV_SAMP";

+--------+------+--------------------------+
| ENAME  | SAL  |       STDDEV_SAMP        |
+--------+------+--------------------------+
| ALLEN  | 1600 | <NULL>                   |
| BLAKE  | 2850 | 841.13019206303610131024 |
| MARTIN | 1250 | 759.79712204421165908596 |
| WARD   | 1250 | 247.4873734152916335403  |
+--------+------+--------------------------+