VARIANCE

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功能描述

计算数据的方差。
可以作为聚合函数或分析函数使用。VARIANCE函数同VAR函数。

语法格式

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

输入参数

• expr：DOUBLE，INTEGER和所有INTERVAL类型，用来指定输入数据。
• 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，输入参数为NULL，返回NULL，当输入只有一行时，返回0。

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),
    (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);

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

+------------------------------+
|           VARIANCE           |
+------------------------------+
| 1398313.87362637362637362637 |
+------------------------------+

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

+--------+------+-----------------------------+
| ENAME  | SAL  |          VARIANCE           |
+--------+------+-----------------------------+
| ALLEN  | 1600 | 0                           |
| WARD   | 1250 | 61250                       |
| BLAKE  | 2850 | 707500                      |
| TURNER | 1500 | 511666.66666666666666666667 |
| MARTIN | 1250 | 444250                      |
| JAMES  | 950  | 446666.66666666666666666667 |
+--------+------+-----------------------------+