The WHERE clause cannot be used to restrict groups. The SELECT statement on the slide results in an error because it uses the WHERE clause to restrict the display of average salaries of those departments that have an average salary greater than $8,000.
You can correct the slide error by using the HAVING clause to restrict groups.
SELECT department_id, AVG(salary)
FROM employees
HAVING AVG(salary) > 8000
GROUP BY department_id;