MySQL Aggregate Functions

 MySQL Aggregate Functions

Summary: in this tutorial, you will learn about MySQL aggregate functions including AVG COUNT, SUM, MAX and MIN.

Introduction to MySQL aggregate functions

An aggregate function performs a calculation on multiple values and returns a single value.

For example, you can use the AVG() an aggregate function that takes multiple numbers and returns the average value of the numbers.

The following illustrates the syntax of an aggregate function:

function_name(DISTINCT | ALL expression)

In this syntax:

• First, specify the name of the aggregate function e.g., AVG(). See the list of aggregate functions in the following section.
• Second, use DISTINCT if you want to calculate based on distinct values or ALL in case you want to calculate all values including duplicates. The default is ALL.
• Third, specify an expression that can be a column or expression which involves column and arithmetic operators.

The aggregate functions are often used with the GROUP BY clause to calculate an aggregate value for each group e.g., the average value by the group or the sum of values in each group.

The following picture illustrates the SUM() an aggregate function is used in conjunction with a GROUP BY clause:

MySQL supports the following aggregate functions:

Aggregate function	Description
AVG()	Return the average of non-NULL values.
BIT_AND()	Return bitwise AND.
BIT_OR()	Return bitwise OR.
BIT_XOR()	Return bitwise XOR.
COUNT()	Return the number of rows in a group, including rows with NULL values.
GROUP_CONCAT()	Return a concatenated string.
JSON_ARRAYAGG()	Return result set as a single JSON array.
JSON_OBJECTAGG()	Return result set as a single JSON object.
MAX()	Return the highest value (maximum) in a set of non-NULL values.
MIN()	Return the lowest value (minimum) in a set of non-NULL values.
STDEV()	Return the population standard deviation.
STDDEV_POP()	Return the population standard deviation.
STDDEV_SAMP()	Return the sample standard deviation.
SUM()	Return the summation of all non-NULL values a set.
VAR_POP()	Return the population standard variance.
VARP_SAM()	Return the sample variance.
VARIANCE()	Return the population standard variance.

MySQL aggregate function examples

We will use the products and orderdetails tables from the sample database for demonstration:

MySQL aggregate function – AVG() function examples

The AVG() the function calculates the average value of a set of values. It ignores NULL in the calculation.

AVG(expression)

For example, you can use the AVG function to calculate the average buy price of all products in the products table by using the following query:

SELECT 
    AVG(buyPrice) average_buy_price
FROM 
    products;

The following example uses the AVG() function to calculate the average buy price for each product line:

SELECT 
    productLine, 
    AVG(buyPrice)
FROM
    products
GROUP BY productLine
ORDER BY productLine;

MySQL aggregate function – COUNT() function examples

The COUNT() the function returns the number of the value in a set.

For example, you can use the COUNT() function to get the number of products in the products table as shown in the following query:

SELECT 
    COUNT(*) AS total
FROM 
    products;

The following statement uses the COUNT() function with the GROUP BY clause to get the number of products for each product line:

SELECT 
    productLine, 
    COUNT(*)
FROM
    products
GROUP BY productLine
ORDER BY productLine;

MySQL aggregate function – SUM() function examples

The SUM() the function returns the sum of values in a set. The SUM() function ignores NULL. If no matching row is found, then SUM() function returns NULL.

To get the total order value of each product, you can use the SUM() function in conjunction with the GROUP BY clause as follows:

SELECT 
    productCode, 
    SUM(priceEach * quantityOrdered) total
FROM
    orderDetails
GROUP BY productCode
ORDER BY total DESC;

To see the result in more detail, you can join the orderdetails table to the products table as shown in the following query:

SELECT 
    productCode,
    productName,
    SUM(priceEach * quantityOrdered) total
FROM
    orderDetails
        INNER JOIN
    products USING (productCode)
GROUP BY productCode
ORDER BY total;

MySQL aggregate function – MAX() function examples

The MAX() the function returns the maximum value in a set.

MAX(expression)

For example, you can use the MAX() function to get the highest buy price from the products table as shown in the following query:

SELECT 
     MAX(buyPrice) highest_price
FROM 
     products;

The following statement uses the MAX() function with the GROUP BY clause to get the highest price per product line:

SELECT 
    productLine, MAX(buyPrice)
FROM
    products
GROUP BY productLine
ORDER BY MAX(buyPrice) DESC;

MySQL aggregate function – MIN() function examples

The MIN() the function returns the minimum value in a set of values.

MIN(expression)

For example, the following query uses the MIN() function to find the lowest price from the products table:

SELECT 
    MIN(buyPrice) lowest_price
FROM 
    products;

The following example uses the MIN() function with the GROUP BY clause to get the lowest price per product line:

SELECT 
    productLine, 
    MIN(buyPrice)
FROM
    products
GROUP BY productLine
ORDER BY MIN(buyPrice);

MySQL aggregate function – GROUP_CONCAT() function example

The GROUP_CONCAT() concatenates a set of strings and returns the concatenated string. See the following employees and customers tables:

The following statement uses the GROUP_CONCAT() function to return the sales staff and list of customers that each sales staff is in charge of:

SELECT 
    firstName,
    lastName,
    GROUP_CONCAT(
	DISTINCT customername
        ORDER BY customerName) customers
FROM
    employees
INNER JOIN customers 
	ON customers.salesRepEmployeeNumber = employeeNumber
GROUP BY employeeNumber
ORDER BY firstName , lastname;

In this tutorial, you have learned how to use the most commonly used MySQL aggregate functions