题解 | #统计各个部门的工资记录数#

select 
d2.dept_no, dept_name, sum
from
(select dept_no, count(*) sum from salaries s left join dept_emp d1
on s.emp_no = d1.emp_no
group by dept_no) d2 left join departments d3 on d2.dept_no = d3.dept_no
order by dept_no asc;