题解 | #汇总各个部门当前员工的title类型的分配数目#

# 部门员工表
select a.dept_no as dept_no
,a.dept_name as dept_name
,b.title as title 
,count(b.title) as count_n
from (select de.dept_no,de.dept_name,dem.emp_no
from departments de 
join dept_emp dem
on de.dept_no = dem.dept_no)a
join 
(select t.emp_no,t.title
from titles t 
)b
on a.emp_no = b.emp_no 
group by a.dept_no,b.title
order by dept_no,title