题解 | #统计各个部门的工资记录数#

先关联 再分组

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