题解 | #统计各个部门的工资记录数#

select
    d2.dept_no,
    dept_name,
    find.sum
from
    departments as d2
    inner join (
        select
            d1.dept_no,
            count(salary) as sum
        from
            departments as d1
            inner join dept_emp de on d1.dept_no = de.dept_no
            inner join salaries s on de.emp_no = s.emp_no
        group by
            1
    ) as find on d2.dept_no = find.dept_no