SQL Aggregate Functions – MIN, MAX, COUNT, SUM, AVG with Examples (2026)

✅ What are SQL Aggregate Functions?

✅ Aggregate functions compute a single result from multiple rows — they summarise your data.

✅ They are used in the SELECT clause and work on a set of rows (the whole table or per group with GROUP BY).

✅ Most aggregate functions automatically ignore NULL values (except COUNT(*)).

✅ Sample Employees Table used in all examples:-

✅ The 5 Main Aggregate Functions at a Glance

✅ MIN() – Find the Lowest Value

MIN() returns the smallest value in a column — works with numbers, text (alphabetical), and dates.

✅ SELECT Query:-

SELECT MIN(Salary) AS MinSalary FROM Employees;

✅ Result:-

✅ MAX() – Find the Highest Value

MAX() returns the largest value in a column.

✅ SELECT Query:-

SELECT MAX(Salary) AS MaxSalary FROM Employees;

✅ Result:-

✅ COUNT() – Count the Number of Rows

COUNT() returns the number of rows. COUNT(*) counts all rows including NULLs; COUNT(column) counts only non-NULL values.

✅ SELECT Query:-

-- Count all rows:
SELECT COUNT(*) AS TotalEmployees FROM Employees;

-- Count only non-NULL bonus values:
SELECT COUNT(Bonus) AS EmployeesWithBonus FROM Employees;

✅ Result:-

✅ SUM() – Calculate the Total

SUM() returns the total sum of all non-NULL values in a numeric column.

✅ SELECT Query:-

SELECT SUM(Salary) AS TotalPayroll FROM Employees;

✅ Result:-

✅ AVG() – Calculate the Average

AVG() returns the average (mean) of all non-NULL values in a numeric column.

✅ SELECT Query:-

SELECT AVG(Salary) AS AvgSalary FROM Employees;

✅ Result:-

✅ All 5 Functions in One Query

You can use multiple aggregate functions in a single SELECT statement.

✅ SELECT Query:-

SELECT
  MIN(Salary)   AS MinSalary,
  MAX(Salary)   AS MaxSalary,
  COUNT(*)      AS TotalEmployees,
  SUM(Salary)   AS TotalPayroll,
  AVG(Salary)   AS AvgSalary
FROM Employees;

✅ Result:-

✅ Aggregate Functions with GROUP BY

Combine aggregate functions with GROUP BY to calculate statistics per group — such as total salary per department.

✅ SELECT Query:-

SELECT Department,
       COUNT(*)      AS Employees,
       MIN(Salary)   AS MinSalary,
       MAX(Salary)   AS MaxSalary,
       SUM(Salary)   AS TotalSalary,
       AVG(Salary)   AS AvgSalary
FROM Employees
GROUP BY Department;

✅ Result:-

✅ How Aggregate Functions Handle NULL

✅ WHERE vs HAVING with Aggregate Functions

Both filter rows, but they operate at different stages of the query:

✅ Example — Departments where total salary exceeds 50000:-

SELECT Department, SUM(Salary) AS TotalSalary
FROM Employees
GROUP BY Department
HAVING SUM(Salary) > 50000;

✅ Result:-

✅ Key Points to Remember

✅ MIN() — smallest value; works on numbers, text, and dates.

✅ MAX() — largest value; works on numbers, text, and dates.

✅ COUNT(*) — counts ALL rows including NULLs.

✅ COUNT(column) — counts only non-NULL values in that column.

✅ SUM() — total of non-NULL numeric values only.

✅ AVG() — average of non-NULL values; divides by non-NULL count.

✅ Always alias results — AS MinSalary makes output column names readable.

✅ GROUP BY — calculates aggregates per group/category.

✅ HAVING — filters groups after aggregation (use HAVING for aggregate conditions, WHERE for row conditions).

✅ Clause order — SELECT → FROM → WHERE → GROUP BY → HAVING → ORDER BY → LIMIT.

✅ Common SQL Aggregate Function Mistakes to Avoid