题解 | #汇总各个部门当前员工的title类型的分配数目#

select d.* ,t.title ,count(title) as count from departments as d 
inner join dept_emp on d.dept_no = dept_emp.dept_no
inner join titles as t on t.emp_no = dept_emp.emp_no
group by d.dept_no,t.title

1.先连表查询汇总所用需用数据
2.通过dept_no和title同时分组