Aggregate functions are used to perform calculations on multiple values and return it to as a single column value.

There are 5 types of ISO standard aggregate functions:

1. COUNT
2. SUM
3. AVG
4. MAX
5. MIN

COUNT:

Example:

Query to find total rows in table

SELECT COUNT(*) AS Total FROM employees;

SUM

Example:

Query to find total salary in IT department

SELECT SUM(salary) FROM employees WHERE Department='IT';

AVG

Example:

Query to find average salary of IT department:

SELECT AVG(salary) FROM employees WHERE Department='IT';

MAX

Example:

Query to get the max amount of salary:

SELECT MAX(Salary) FROM employees

Query to find who get the max salary in all departments:

SELECT FirstName,LastName,Department,Salary FROM employees WHERE Salary=(SELECT MAX(Salary) FROM employees);

MIN

Example:

Query to find min amount of salary:

SELECT MIN(Salary) FROM employees;

Query to find who get the min salary in all departments:

SELECT FirstName,LastName,Department,Salary FROM employees WHERE Salary=(SELECT MIN(Salary) FROM employees);