题解 | 汇总各个部门当前员工的title类型的分配数目

select d.dept_no,d.dept_name,t.title,count(t.title) as count 
from titles t 
left join (
    select d1.emp_no as emp_no,d1.dept_no as dept_no,d2.dept_name as dept_name
    from dept_emp d1
    left join departments d2
    on d1.dept_no = d2.dept_no
    where d1.to_date = "9999-01-01") d
on t.emp_no = d.emp_no 
where t.to_date = "9999-01-01"
group by d.dept_no,t.title
order by d.dept_no;