VARIANCE

说明

计算方差。

语法

variance ::=

参数

analytic_clause

一个分析语句（包含分区、排序、窗口信息）。详细说明参见 分析函数 一节。

返回值

计算出的方差。

示例

示例1: 计算方差

--  清理环境
DROP TABLE tab1 CASCADE;

--  创建表并插入数据
create table tab1(id INT, a INT, b INT);

INSERT INTO tab1 VALUES(1, 21, 55);
INSERT INTO tab1 VALUES(2, 21, 56);
INSERT INTO tab1 VALUES(3, 21, 48);
INSERT INTO tab1 VALUES(4, 22, 70);
INSERT INTO tab1 VALUES(5, 22, 65);
INSERT INTO tab1 VALUES(6, 11, 40);
INSERT INTO tab1 VALUES(7, 11, 43);
INSERT INTO tab1 VALUES(8, 31, 77);
INSERT INTO tab1 VALUES(9, 32, 80);


SELECT * FROM tab1 ORDER BY id;
ID(int)      |A(int)      |B(int)      |
-------------------------------------
1            |21          |55          |
-------------------------------------
2            |21          |56          |
-------------------------------------
3            |21          |48          |
-------------------------------------
4            |22          |70          |
-------------------------------------
5            |22          |65          |
-------------------------------------
6            |11          |40          |
-------------------------------------
7            |11          |43          |
-------------------------------------
8            |31          |77          |
-------------------------------------
9            |32          |80          |
总数目：9


--  计算方差
SELECT id, a, b, VARIANCE(b) OVER (PARTITION BY a) FROM tab1 ORDER BY id;
ID(int)      |A(int)      |B(int)      |VARIANCE(numeric)      |
------------------------------------------------------------
1            |21          |55          |19                     |
------------------------------------------------------------
2            |21          |56          |19                     |
------------------------------------------------------------
3            |21          |48          |19                     |
------------------------------------------------------------
4            |22          |70          |12.5                   |
------------------------------------------------------------
5            |22          |65          |12.5                   |
------------------------------------------------------------
6            |11          |40          |4.5                    |
------------------------------------------------------------
7            |11          |43          |4.5                    |
------------------------------------------------------------
8            |31          |77          |0                      |
------------------------------------------------------------
9            |32          |80          |0                      |
总数目：9

--  删除表
DROP TABLE tab1;