题解 | 统计各个部门的工资记录数

select
    b.dept_no,
    a.dept_name,
    count(c.salary) as sum
from
    salaries c
    left join dept_emp b using (emp_no)
    left join departments a using (dept_no)
group by
    b.dept_no,
    a.dept_name
order by  b.dept_no asc