STDDEV Function - SQL

Overview

The STDDEV function in SQL calculates the standard deviation of values in a specified numeric column, which measures the amount of variation or dispersion in the dataset. It is commonly used in SELECT statements to analyze the spread of data points around the mean, optionally filtered by a condition.

Example:

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

Syntax:

SELECT STDDEV(column_name)
FROM table_name
[WHERE condition]

This calculates the standard deviation 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 STDDEV function will calculate the standard deviation 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 standard deviation of the salary column in the company.employees table. The final output is 27180.87.

Example: With the WHERE Statement

In this example, we are returning the standard deviation of the salary column in the company.employees table where the department_id column equals 1. The final output is 8498.36.