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SQL Aggregate functions - GeeksforGeeks

Last Updated : 02 Aug, 2025

SQL Aggregate Functions are used to perform calculations on a set of rows and return a single value. These functions are particularly useful when we need to summarize, analyze, or group large datasets in SQL databases.

They are often used with the GROUP BY clause in SQL to summarize data for each group. Commonly used aggregate functions include COUNT(), SUM(), AVG(), MIN() and MAX().

• Operate on groups of rows: They work on a set of rows and return a single value.
• Ignore NULLs: Most aggregate functions ignore NULL values, except for COUNT(*).
• Used with GROUP BY: To perform calculations on grouped data, you often use aggregate functions with GROUP BY.
• Can be combined with other SQL clauses: Aggregate functions can be used alongside HAVING, ORDER BY and other SQL clauses to filter or sort results.

Below are the most frequently used aggregate functions in SQL.

The COUNT() function returns the number of rows that match a given condition or are present in a column.

• COUNT(*): Counts all rows.
• COUNT(column_name): Counts non-NULL values in the specified column.
• COUNT(DISTINCT column_name): Counts unique non-NULL values in the column.

Examples:

-- Total number of records in the table
SELECT COUNT(*) AS TotalRecords FROM Employee;

-- Count of non-NULL salaries

SELECT COUNT(Salary) AS NonNullSalaries FROM Employee;

-- Count of unique non-NULL salaries

SELECT COUNT(DISTINCT Salary) AS UniqueSalaries FROM Employee;

The SUM() function calculates the total sum of a numeric column.
SUM(column_name): Returns the total sum of all non-NULL values in a column.

Examples:

-- Calculate the total salary
SELECT SUM(Salary) AS TotalSalary FROM Employee;

-- Calculate the sum of unique salaries

SELECT SUM(DISTINCT Salary) AS DistinctSalarySum FROM Employee;

The AVG() function calculates the average of a numeric column. It divides the sum of the column by the number of non-NULL rows.
AVG(column_name): Returns the average of the non-NULL values in the column.

Examples:

-- Calculate the average salary
SELECT AVG(Salary) AS AverageSalary FROM Employee;

-- Average of distinct salaries

SELECT AVG(DISTINCT Salary) AS DistinctAvgSalary FROM Employee;

The MIN() and MAX() functions return the smallest and largest values, respectively, from a column.

• MIN(column_name): Returns the minimum value.
• MAX(column_name): Returns the maximum value.

Examples:

-- Find the highest salary
SELECT MAX(Salary) AS HighestSalary FROM Employee;

-- Find the lowest salary

SELECT MIN(Salary) AS LowestSalary FROM Employee;

Let's consider a demo Employee table to demonstrate SQL aggregate functions . This table contains employee details such as their ID, Name, and Salary.

SELECT COUNT(*) AS TotalEmployees FROM Employee;

Output:

SELECT SUM(Salary) AS TotalSalary FROM Employee;

Output:

SELECT AVG(Salary) AS AverageSalary FROM Employee;

Output:

SELECT MAX(Salary) AS HighestSalary FROM Employee;

Output:

SQL GROUP BY allows us to group rows that have the same values in specific columns. We can then apply aggregate functions to these groups, which helps us summarize data for each group. This is commonly used with the COUNT(), SUM(), AVG(), MIN(), and MAX() functions.

SELECT Name, SUM(Salary) AS TotalSalary
FROM Employee
GROUP BY Name;

Output:

The HAVING clause is used to filter results after applying aggregate functions, unlike WHERE, which filters rows before aggregation. HAVING is essential when we want to filter based on the result of an aggregate function.

SELECT Name, SUM(Salary) AS TotalSalary
FROM Employee
GROUP BY Name
HAVING SUM(Salary) > 600;

Output:

Aggregate Functions and GROUP BY Statement in SQL

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