Answer
The average salary per department is calculated with AVG and GROUP BY. • GROUP BY creates one result group per department. • AVG ignores null salary values. • Join departments when the output also needs department names or empty departments.
💡 SQL Example
SELECT department_id, AVG(salary) AS average_salary FROM employees GROUP BY department_id;
Result
One average salary per department
⚡ Quick Revision
Group by department and apply AVG to salary.