SELECT
    dm.dept_no,
    dm.dept_name,
    COUNT(*) AS sum
FROM
    departments AS dm
    INNER JOIN
    dept_emp AS de ON dm.dept_no=de.dept_no
        INNER JOIN
        salaries AS s ON de.emp_no=s.emp_no 
GROUP BY
    dm.dept_no,
    dm.dept_name
ORDER BY
    dm.dept_no ASC;