MySQL - STDDEV() Function

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The MySQL STDDEV() function calculates and returns the population standard deviation of all the values in a particular column.

Standard deviation is the square root of the average of squared deviations of the items from their mean. Symbolically it is represented by σσ.

If the specified row(s) doesn't exist this function returns NULL.

Syntax

Following is the syntax of MySQL STDDEV() function −

STDDEV(expr);

Parameters

This method accepts a parameter. The same is described below −

• expr: An expression or a particular column for which we want to calculate the population standard deviation.

Return value

This function calculates and returns the population standard deviation for the rows in a particular column.

Example

First of all, let us create a table named CUSTOMERS using the CREATE statement as follows −

CREATE TABLE CUSTOMERS (
   ID INT AUTO_INCREMENT,
   NAME VARCHAR(20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),
   PRIMARY KEY (ID)
);

The following query inserts 7 records into the above created table −

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES 
(1, 'Ramesh', 32, 'Ahmedabad', 2000.00 ),
(2, 'Khilan', 25, 'Delhi', 1500.00 ),
(3, 'Kaushik', 23, 'Kota', 2000.00 ),
(4, 'Chaitali', 25, 'Mumbai', 6500.00 ),
(5, 'Hardik', 27, 'Bhopal', 8500.00 ),
(6, 'Komal', 22, 'Hyderabad', 4500.00 ),
(7, 'Muffy', 24, 'Indore', 10000.00 );

Execute the following query to verify whether the records are inserted into CUSTOMERS table −

Select * From CUSTOMERS;

Following is the CUSTOMERS table −

ID	NAME	AGE	ADDRESS	SALARY
1	Ramesh	32	Ahmedabad	2000.00
2	Khilan	25	Delhi	1500.00
3	Kaushik	23	Kota	2000.00
4	Chaitali	25	Mumbai	6500.00
5	Hardik	27	Bhopal	8500.00
6	Komal	22	Hyderabad	4500.00
7	Muffy	24	Indore	10000.00

Here, we are using the MySQL STDDEV() function to calculate the population standard deviation of salaries of all the customers −

SELECT STDDEV(SALARY) From CUSTOMERS;

Output

This will produce the following result −

STD(SALARY)
3162.2776601683795

The result of the query will be NULL because there are no records in the CUSTOMERS table where the ID is equal to 10 −

SELECT STD(SALARY) From CUSTOMERS
WHERE ID = 10;

Output

This will produce the following result −

STD(SALARY)
NULL