题解 | #统计各个部门的工资记录数#

select d.dept_no,d.dept_name,count(*) sum 
from
(departments d inner join dept_emp de 
on d.dept_no=de.dept_no) t inner join salaries s 
on t.emp_no=s.emp_no
group by d.dept_no
order by d.dept_no;