select dept_emp.dept_no as dept_no,departments.dept_name as dept_name,titles.title as title ,count(s1.emp_no)
from (dept_emp left join departments on dept_emp.dept_no=departments.dept_no left join titles on dept_emp.emp_no=titles.emp_no)as s1
group by s1.dept_no,s1.title
order by dept_emp.dept_no asc
这道题终于通过了，同时对“dept_no”和“title”进行group by，在用count就可以统计出来了