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

SQL221 统计各个部门的工资记录数

select dept_no,dept_name 2个字段

则group by 也需要2个字段