题解 | 汇总各个部门当前员工的title类型的分配数目

select t.dept_no, t.dept_name, t.title, count(t.title) as count
from (
    select de.*, ts.title, dm.dept_name
    from dept_emp de
    left join titles ts
    on de.emp_no = ts.emp_no
    left join departments dm
    on de.dept_no = dm.dept_no
) t
group by t.dept_no, t.title
order by t.dept_no, t.title