运行结果正确，可以稳定运行
select dept_no,dept_name,count(dept_no)
from (
select emp_no,dept_emp.dept_no,departments.dept_name
from dept_emp left join departments
on dept_emp.dept_no=departments.dept_no
) as j
left join salaries on j.emp_no=salaries.emp_no
group by (dept_no)
order by (dept_no)