题解 | 统计各个部门的工资记录数

select
    t1.dept_no,
    dp.dept_name,
    t1.sum
from
    (
        select
            de.dept_no,
            count(s.salary) as sum
        from
            salaries s
            join dept_emp de on de.emp_no = s.emp_no
        group by
            de.dept_no
    ) as t1
    join departments dp on dp.dept_no = t1.dept_no
order by
    dept_no;
	
select
    dp.dept_no,
    dp.dept_name,
    count(s.salary)
from
    salaries s
    join dept_emp de on s.emp_no = de.emp_no
    join departments dp on dp.dept_no = de.dept_no
group by
    dp.dept_no,
    dp.dept_name
order by
    dept_no;