Purpose
VARIANCE() returns the variance from the specified column. You can use this function as an aggregate or analytic function.
Note
- When you use this function as an analytic function, use the
OVERclause to define a window over the data on which the function operates. The function operates on a group of rows to return a list of values. - When you use this function as an aggregate function, the function operates on a set of rows and returns a single value. You do not need to add the
OVERclause.
Syntax
VARIANCE([ DISTINCT | UNIQUE | ALL ] expr) [ OVER (analytic_clause) ]
Parameters
| Parameter | Description |
|---|---|
| DISTINCT | UNIQUE | ALL | Specifies whether to remove duplicates during the execution of the query. This parameter is optional. Default value: ALL.
|
| expr | An expression of a numeric data type or a data type that can be implicitly converted to a numeric data type. |
| OVER | You can use the OVER clause to define a window over the data on which the function operates. For more information, see Analytic functions. |
Notice
If you specify the DISTINCT or UNIQUE keyword, you can specify only analytic_clause. order_by_clause and windowing_clause are not allowed.
Return type
The return type is the same as the data type of the expr parameter.
Examples
Assume that you have created the table employees.
obclient> SELECT * FROM employees;
+---------------+-----------+------------+--------+
| DEPARTMENT_ID | LAST_NAME | HIREDATE | SALARY |
+---------------+-----------+------------+--------+
| 30 | Raphaely | 2017-07-01 | 1700 |
| 30 | De Haan | 2018-05-01 | 11000 |
| 40 | Errazuriz | 2017-07-21 | 1400 |
| 50 | Hartstein | 2019-10-05 | 14000 |
| 50 | Raphaely | 2017-07-22 | 1700 |
| 50 | Weiss | 2019-10-05 | 13500 |
| 90 | Russell | 2019-07-11 | 13000 |
| 90 | Partners | 2018-12-01 | 14000 |
+---------------+-----------+------------+--------+
8 rows in set
Example of an aggregate function
Calculate the variance of all values in the salary column.
obclient> SELECT SUM(salary) FROM employees;
+-------------+
| SUM(SALARY) |
+-------------+
| 70300 |
+-------------+
1 row in set
Example of an analytic function
Sort the data records in the table by the hiredate column in ascending order, and return the cumulative variance for the salary column.
obclient> SELECT last_name,hiredate,salary,VARIANCE(salary) OVER (ORDER BY hiredate) "Variance"
FROM employees;
+-----------+------------+--------+-------------------------------------------+
| LAST_NAME | HIREDATE | SALARY | Variance |
+-----------+------------+--------+-------------------------------------------+
| Raphaely | 2017-07-01 | 1700 | 0 |
| Errazuriz | 2017-07-21 | 1400 | 45000 |
| Raphaely | 2017-07-22 | 1700 | 30000 |
| De Haan | 2018-05-01 | 11000 | 22110000 |
| Partners | 2018-12-01 | 14000 | 36783000 |
| Russell | 2019-07-11 | 13000 | 37686666.6666666666666666666666666666666 |
| Hartstein | 2019-10-05 | 14000 | 36318392.85714285714285714285714285714286 |
| Weiss | 2019-10-05 | 13500 | 36318392.85714285714285714285714285714286 |
+-----------+------------+--------+-------------------------------------------+
8 rows in set
