SQL - VARP() Function

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The SQL VARP() function calculates the population standard variance of the fields (numerical values) in a particular column. If the specified row(s) doesn't exist, then this function returns NULL.

The population standard variance is a measure of the amount of variation or dispersion in a set of data from its mean value. Mathematically, the mean is an average value of given set of number and a variance is defined as the average of squared differences from mean value. Symbolically it is represented by σ².

Syntax

Following is the syntax of SQL VARP() function −

VARP(column_name)

Parameters

• column_name − It is the name of the column for which we want to calculate the standard deviation variance for the population.

Example

Assume we have created a table with name CUSTOMERS as shown below −

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

Let us insert values into it −

insert INTO CUSTOMERS VALUES(1, 'Ramesh', 32, 'Ahmedabad', 2000.00);
insert INTO CUSTOMERS VALUES(2, 'Khilan', 25, 'Delhi', 1500.00);
insert INTO CUSTOMERS VALUES(3, 'kaushik', 23, 'Kota', 2000.00);
insert INTO CUSTOMERS VALUES(4, 'Chaitali', 25, 'Mumbai', 6500.00);
insert INTO CUSTOMERS VALUES(5, 'Hardik', 27, 'Bhopal', 8500.00);
insert INTO CUSTOMERS VALUES(6, 'Komal', 22, 'MP', 4500.00);
insert INTO CUSTOMERS VALUES(7, 'Muffy', 24, 'Indore', 10000.00);

If you retrieve the table using the select statement, you will get the following output −

+----+----------+-----+-----------+----------+
| 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 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

Following query calculates the population standard variance of salary of all the customers −

SELECT VARP(SALARY) as st_varp
from CUSTOMERS

Output

+------------------+
| st_varp          |
+------------------+
| 10000000         |
+------------------+

Example

The following query returns all the customers whose salary is greater than the square root of salary population standard variance −

SELECT NAME, SALARY, AGE,ADDRESS
FROM CUSTOMERS
WHERE SALARY > (SELECT SQRT(VARP(SALARY)) FROM CUSTOMERS)

Since, we all know from the above example that the square root of salary population standard variance is approximately equals to 3162.27. Hence, while executing the above code we get the following output −

Output

+----------+----------+-----+---------+
| NAME     | SALARY   | AGE | ADDRESS |
+----------+----------+-----+---------+
| Chaitali |  6500.00 |  25 | Mumbai  |
| Hardik   |  8500.00 |  27 | Bhopal  |
| Komal    |  4500.00 |  22 | MP      |
| Muffy    | 10000.00 |  24 | Indore  |
+----------+----------+-----+---------+

Example

Now, suppose based on the above table we want to calculate the population standard variance of distinct (unique) age of the customers, then we can do so simply using the following query −

SELECT VARP(DISTINCT AGE) as st_varp
from CUSTOMERS

Output

+------------------+
| st_varp          |
+------------------+
| 10.9166666666667 |
+------------------+

Example

In here, we are trying to get the Population standard variance of salary of all customers whose age is greater than 24 −

SELECT VARP(Salary) AS st_varp
FROM CUSTOMERS
WHERE AGE > 24;

Output

+------------------+
| st_varp          |
+------------------+
| 8796875          |
+------------------+