-- solved with join
SELECT d.department_name, SUM(e.salary) AS dept_total
FROM employees e
     JOIN departments d
     ON (e.department_id = d.department_id)
GROUP BY d.department_name
HAVING SUM(e.salary) > (SELECT SUM(salary)
                        FROM employees) / 8   -- cannot put sum(...) into WHERE!!!
ORDER BY d.department_name;