题解 |join+group by+order by解决问题

select
    d.dept_no,
    d.dept_name,
    t.title,
    count(t.title) count
from
    departments d
    left join dept_emp e on d.dept_no = e.dept_no
    left join titles t on e.emp_no = t.emp_no
group by
    d.dept_no,
    d.dept_name,
    t.title
order by
    d.dept_no,
    t.title asc