STDDEV() function in MySQL

Sometimes we need to calculate population Standard deviation of an expression in MySQL. STDDEV() function can be used for this purpose in MySQL. It returns NULL if no matching rows found in the given expression. Syntax :

STDDEV(expr);

Parameter : This method accepts only one parameter.

• expr : Input expression from which we want to calculate standard deviation .

Returns : It returns the population standard deviation. Example-1 : Finding standard deviation of sub1mark column from the given StudentMarks table using STDDEV Function. Creating a StudentMarks table :

CREATE TABLE StudentMarks
(
StudentId INT AUTO_INCREMENT,  
StudentName VARCHAR(100) NOT NULL,
Roll INT NOT NULL,
Sub1Mark INT NOT NULL,
Sub2Mark INT NOT NULL,
Sub3Mark INT NOT NULL,
TotalMarks INT NOT NULL,
PRIMARY KEY(StudentId )
);

Inserting data into the Table :

INSERT INTO StudentMarks
(StudentName, Roll, Sub1Mark, Sub2Mark, Sub3Mark, TotalMarks)
VALUES
('Amit Jana', 10100, 85, 80, 95, 260),
('Labanya Mallick', 11000, 81, 89, 95, 265),
('Virat Sharma', 12000, 75, 83, 90, 248),
('Sayani Samanta', 13000, 95, 90, 99, 284),
('Riyanka Panda', 14000, 70, 87, 88, 245),  
('Ritika Shah', 15000, 78, 89, 90, 257);

To verify used the following command as follows.

SELECT  * from StudentMarks;

Output :

STUDENTID	STUDENTNAME	ROLL	SUB1MARK	SUB2MARK	SUB3MARK	TOTALMARKS
1	Amit Jana	10100	85	80	95	260
2	Labanya Mallick	11000	81	89	95	265
3	Virat Sharma	12000	75	83	90	248
4	Sayani Samanta	13000	95	90	99	284
5	Riyanka Panda	14000	70	87	88	245
6	Ritika Shah	15000	78	89	90	257

Now we are going to find standard deviation of sub1mark column.

SELECT  STDDEV(Sub1Mark) as Sub1StandardDeviation  
FROM StudentMarks;

Output :

SUB1STANDARDDEVIATION
7.930251502246881

Example-2

Now we are going to find population standard deviation of total marks column.

SELECT  STDDEV(TotalMarks) as StdDevOfTotalMarks  
FROM StudentMarks;

Output :

STDDEVOFTOTALMARKS
12.772583485297279

Example-3 : In this example we are going to find the population standard deviation of Income of Employee who are working in the company 'XYZ Digital'. To demonstrate create a table named EmloyeeDetails.

CREATE TABLE EmployeeDetails(

    Employee_Id INT AUTO_INCREMENT,  
    Employee_Name VARCHAR(100) NOT NULL,
    Working_At VARCHAR(20) NOT NULL,
    Work_Location  VARCHAR(20) NOT NULL,
    Joining_Date DATE NOT NULL,
    Annual_Income INT  NOT NULL,
    PRIMARY KEY(Employee_Id )
);

Inserting data into the Table :

INSERT INTO  
    EmployeeDetails(Employee_Name, Working_At, Work_Location, Joining_Date, Annual_Income )

VALUES
    ('Amit Khan', 'XYZ Digital', 'Kolkata', '2019-10-06', 350000 ),
    ('Shreetama Pal', 'ABC Corp.', 'Kolkata', '2018-12-16', 500000 ),
    ('Aniket Sharma', 'PQR Soln.', 'Delhi', '2020-01-11', 300000 ),
    ('Maitree Jana', 'XYZ Digital', 'Kolkata', '2019-05-01', 400000 ),
    ('Priyanka Ojha', 'ABC Corp.', 'Delhi', '2019-02-13', 350000 ),
    ('Sayani Mitra', 'XYZ Digital', 'Kolkata', '2019-09-15', 320000 ),
    ('Nitin Dey', 'PQR Soln.', 'Delhi', '2019-10-06', 250000 ),
    ('Sujata Samanta', 'PQR Soln.', 'Kolkata', '2020-10-06', 350000 ),
    ('Sudip Majhi', 'ABC Corp.', 'Delhi', '2018-10-30', 600000 ),
    ('Sanjoy Kohli', 'XYZ Digital', 'Delhi', '2019-04-18', 450000 ) ;

To verify used the following command as follows.

Select * FROM EmployeeDetails;

Output :

EMPLOYEE_ID	EMPLOYEE_NAME	WORKING_AT	WORK_LOCATION	JOINING_DATE	ANNUAL_INCOME
1	Amit Khan	XYZ Digital	Kolkata	2019-10-06	350000
2	Shreetama Pal	ABC Corp.	Kolkata	2018-12-16	500000
3	Aniket Sharma	PQR Soln.	Delhi	2020-01-11	300000
4	Maitree Jana	XYZ Digital	Kolkata	2019-05-01	400000
5	Priyanka Ojha	ABC Corp.	Delhi	2019-02-13	350000
6	Sayani Mitra	XYZ Digital	Kolkata	2019-09-15	320000
7	Nitin Dey	PQR Soln.	Delhi	2019-10-06	250000
8	Sujata Samanta	PQR Soln.	Kolkata	2020-10-06	350000
9	Sudip Majhi	ABC Corp.	Delhi	2018-10-30	600000
10	Sanjoy Kohli	XYZ Digital	Delhi	2019-04-18	450000

Now we are going to find population standard deviation of annual Income for those Employee who are working in 'XYZ Digital'.

SELECT  STDDEV(Annual_Income) as StdDevOfAnnualIncome  
FROM EmployeeDetails where WORKING_AT = 'XYZ Digital';

Output :

STDDEVOFANNUALINCOME
49497.474683058324