【MySQL】为什么两种方式下的查询结果不一样？

select department_name, e.manager_id, min(salary) from employees e, departments d where e.`department_id` = d.`department_id` and commission_pct is not null group by e.department_id;

select department_name, d.manager_id, min(salary) from employees e, departments d where e.`department_id` = d.`department_id` and commission_pct is not null group by department_name;

group by的合并方式不同，应该是有多个部门用了同个名字，但是id不同导致的