树叶云OceanBase教程：OceanBase VARIANCE

VARIANCE 函数返回参数指定列的方差。

语法

VARIANCE([ DISTINCT | UNIQUE | 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

注意 

如果您指定了 DISTINCT 或 UNIQUE 关键字，则 analytic_clause 中不允许出现 order_by_clause 和 windowing_clause。

返回类型

返回 NUMBER 类型数据。

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;

执行以下语句计算列 salary 的方差：

SELECT last_name, salary, VARIANCE(salary)  OVER (ORDER BY hiredate) "Variance"
FROM employees WHERE manager_id = 100 ORDER BY last_name, salary, "Variance";

查询结果如下：

+-----------+--------+-------------------------------------------+
| LAST_NAME | SALARY | Variance                                  |
+-----------+--------+-------------------------------------------+
| De Haan   |  11000 |                                  22110000 |
| Errazuriz |   1400 |                                     45000 |
| Hartstein |  14000 |                                  40200000 |
| Partners  |  14000 |                                  36783000 |
| Raphaely  |   1700 |                                         0 |
| Raphaely  |   1700 |                                     30000 |
| Russell   |  13000 | 36318392.85714285714285714285714285714286 |
| Weiss     |  13500 | 38991428.57142857142857142857142857142857 |
+-----------+--------+-------------------------------------------+

聚合函数示例

执行以下语句计算列 salary 的方差：

SELECT VARIANCE(salary)  FROM employees;

查询结果如下：

+-----------------------------------------+
| VARIANCE(SALARY)                        |
+-----------------------------------------+
| 30318181.818181818181818181818181818182 |
+-----------------------------------------+