List the main aggregate functions.

The main aggregate functions in SQL:

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

These functions are often used with GROUP BY to group data and with HAVING to filter grouped results.

Example:

SELECT department, COUNT(*) AS employee_count, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;