VAR_SAMP

功能描述

计算数据的样本方差。

可以作为聚合函数或分析函数使用。

语法格式

VAR_SAMP(expr) [ OVER (analytic_clause) ]

参数说明

• expr：列名或表达式，用来指定输入数据。
• OVER (analytic_clause)：可选的表达式，用于分析函数。analytic_clause：常用的分析类语句，如ORDER BY等。

函数返回类型

NUMERIC/DOUBLE数值类型。

示例

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)
     );

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),
    (7782, 'CLARK', 'MANAGER', 7839, TO_DATE('9-6-1981', 'DD-MM-YYYY'), 2450, NULL, 10),
    (7788, 'SCOTT', 'ANALYST', 7566, TO_DATE('13-7-1987', 'DD-MM-YYYY'), 3000, NULL, 20),
    (7839, 'KING', 'PRESIDENT', NULL, TO_DATE('17-11-1981', 'DD-MM-YYYY'), 5000, NULL, 10),
    (7844, 'TURNER', 'SALESMAN', 7698, TO_DATE('8-9-1981', 'DD-MM-YYYY'), 1500, 0, 30),
    (7876, 'ADAMS', 'CLERK', 7788, TO_DATE('13-7-1987', 'DD-MM-YYYY'), 1100, NULL, 20),
    (7900, 'JAMES', 'CLERK', 7698, TO_DATE('3-12-1981', 'DD-MM-YYYY'), 950, NULL, 30),
    (7902, 'FORD', 'ANALYST', 7566, TO_DATE('3-12-1981', 'DD-MM-YYYY'), 3000, NULL, 20),
    (7934, 'MILLER', 'CLERK', 7782, TO_DATE('23-1-1982', 'DD-MM-YYYY'), 1300, NULL, 10);

聚合函数

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

VAR_SAMP |
------------------------------------------------------------------------------
1398313.87362637362637362637|

分析函数

SQL> SELECT hiredate, VAR_SAMP(SUM(sal)) OVER (ORDER BY hiredate) "VAR_SAMP" FROM employees GROUP BY hiredate ORDER BY hiredate, "VAR_SAMP";

HIREDATE | VAR_SAMP |
------------------------------------------------------------------------------
1980-12-17 AD | <NULL>|
1981-02-20 AD | 320000|
1981-02-22 AD | 160833.33333333333333333333|
1981-04-02 AD | 880156.25|
1981-05-01 AD | 945125|
1981-06-09 AD | 807437.5|
1981-09-08 AD | 706815.47619047619047619048|
1981-09-28 AD | 661595.98214285714285714286|
1981-11-17 AD | 1692361.11111111111111111111|
1981-12-03 AD | 1815451.38888888888888888889|
1982-01-23 AD | 1736534.09090909090909090909|
1987-07-13 AD | 1858991.47727272727272727273|