题解 | #统计各个部门的工资记录数#

select
    de.dept_no,
    de.dept_name,
    b.sum
from
    (
        select
            dept_no,
            count(salary) as sum
        from
            (
                select
                    d.dept_no,
                    s.salary
                from
                    dept_emp as d
                    right join salaries as s on d.emp_no = s.emp_no
            ) as a
        group by
            dept_no
    ) as b
    inner join departments as de on de.dept_no = b.dept_no;