题解 | #统计各个部门的工资记录数#

select dept_no,dept_name,sum from 
departments NATURAL JOIN 
(select dept_no,count(emp_no) as sum from 
(select dept_emp.emp_no,dept_emp.dept_no from dept_emp inner join salaries
on dept_emp.emp_no = salaries.emp_no) as jt
group by dept_no) as t2;