VARIANCE Function - SQL

Overview

The VARIANCE function in SQL calculates the variance of values in a specified numeric column, indicating the degree of spread or dispersion within the dataset. It is commonly used in SELECT statements to measure how much the data points deviate from the mean, optionally filtered by a condition.

Example:

SELECT VARIANCE(salary)
FROM company.employees
WHERE department_id = 1

Syntax:

SELECT VARIANCE(column_name)
FROM table_name
[WHERE condition]

This calculates the variance of the values in column_name from table_name that meet the specified condition. In this syntax, the WHERE Statement is optional; if omitted, the VARIANCE function will calculate the variance for all rows in the table.

Sample Data:

    
            department_id
            salary
        
            3
            123000
        
            2
            135000
        
            3
            115000
        
            NULL
            115000
        
            2
            125000
        
            1
            120000
        
            1
            105000
        
            5
            200000
        
            2
            107000
        
            1
            100000

department_id	salary
3	123000
2	135000
3	115000
NULL	115000
2	125000
1	120000
1	105000
5	200000
2	107000
1	100000

Example: Without the WHERE Statement

In this example, we are returning the variance of the salary column in the company.employees table. The final output is 738800000.

Example: With the WHERE Statement

In this example, we are returning the variance of the salary column in the company.employees table where the department_id column equals 1. The final output is 72222222.22.