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

知识点:
1.三表链接
2. 使用group by 函数进行分组
3. order by 进行排序
4. count()用于统计