这个还挺快的，简单来说，仨表全给连接了提取需要的信息，先后按部门，title分组，部门排序

select c.dept_no,d.dept_name,c.title,count(title)
from
(select a.dept_no,a.emp_no,title
from dept_emp a
join
titles b
on a.emp_no=b.emp_no)c
join departments d
on c.dept_no=d.dept_no
group by c.dept_no,c.title
order by c.dept_no