题解 | #汇总各个部门当前员工的title类型的分配数目#

主要是group by联合分组的考察

select d.dept_no, d.dept_name, t.title, count(*) as count
from departments as d inner join dept_emp as de 
on d.dept_no = de.dept_no and de.to_date = '9999-01-01'
inner join titles as t
on de.emp_no = t.emp_no and t.to_date = '9999-01-01'
group by de.dept_no, t.title
order by de.dept_no
;