只需要搞清楚 分组 就行了
汇总各个部门当前员工的title类型的分配数目
https://www.nowcoder.com/practice/4bcb6a7d3e39423291d2f7bdbbff87f8
select
dm.dept_no,dm.dept_name,tl.title,count(*)
from
departments as dm
join dept_emp as de on dm.dept_no = de.dept_no
join titles as tl on tl.emp_no = de.emp_no
group by
dm.dept_no,dm.dept_name,tl.title
order by
de.dept_no asc,tl.title asc
