select de.dept_no,d.dept_name,count(s.emp_no) as sum from departments as d inner join dept_emp as de on d.dept_no = de .dept_no
inner join salaries as s on s.emp_no = de.emp_no
group by d.dept_name order by de.dept_no
四个知识点:
- count函数(统计总数量)
- 表链接(三表链接)
- group by 对部门名称进行分组
- order by 排序