An aggregate function in SQL performs a calculation on a set of values and returns a single value. Common aggregate functions include COUNT(), SUM(), AVG(), MAX(), and MIN().

Examples of Aggregate Functions:

Assume we have the following employees table:

1. COUNT(): Returns the number of rows that match a specified condition.

SELECT COUNT(*) AS total_employees FROM employees;

 Result:
   total_employees
   ----------------
   5          

2. SUM(): Returns the sum of a numeric column.

SELECT SUM(salary) AS total_salary FROM employees;

 Result:
   total_salary 
   --------------
    31500        

3. AVG(): Returns the average value of a numeric column.

SELECT AVG(salary) AS average_salary FROM employees;

Result:
   average_salary 
   ----------------
    6300       

4. MAX(): Returns the maximum value in a set.

SELECT MAX(salary) AS highest_salary FROM employees;

Result:
  highest_salary 
  ----------------
   8000    

5. MIN(): Returns the minimum value in a set.

SELECT MIN(salary) AS lowest_salary FROM employees;

 Result:
   lowest_salary 
   ---------------
    5000