What are aggregate functions? Provide examples

Aggregate functions perform calculations on a set of values and return a single value. They are often used in combination with the GROUP BY clause.

Key Aggregate Functions

• COUNT() — counts the number of rows.
• SUM() — calculates the sum of values.
• AVG() — calculates the average value.
• MAX() — finds the maximum value.
• MIN() — finds the minimum value.

Examples of usage

1. Counting the number of employees:

MySQL 8.1
SELECT COUNT(*) FROM employees;

2. Average salary by department:

MySQL 8.1
SELECT department_id, AVG(salary) AS average_salary
FROM employees
GROUP BY department_id;

3. Maximum salary in the company:

MySQL 8.1
SELECT MAX(salary) FROM employees;

4. Total sales for the month:

MySQL 8.1
SELECT SUM(amount) FROM sales WHERE sale_date BETWEEN '2023-01-01' AND '2023-01-31';