题解 | #统计各个部门的工资记录数#

select
    d.dept_no,
    d.dept_name,
    count(*) as sum
from
    departments d
    left join dept_emp de on d.dept_no = de.dept_no
    left join salaries s on de.emp_no = s.emp_no
group by
    d.dept_no
order by
    d.dept_no asc