1、<1>/*第一步，查询出员工人数最多的部门的员工人数*/ select max(count(*)) from employeesgroup by department_id
2、<2>/*第二步，员工表和部门表连接，以部门分组，*/ select dept.department_id,dept.department_name,count(*),e1.first_name||e1.last_name from departments dept,employees e ,employees e1 where dept.department_id=e.department_id and dept.manager_id=e1.employee_id group bydept.department_id,dept.department_name,e1.first_name||e1.last_name
3、<3> /*第三部，合并一二两部，讲第一步查询出来的结果作为第二部分组完的条件*/ select dept.department_足毂忍珩id,dept.department_name,count(*),e1.first_name||e1.last_name from departments dept,employees e ,employees e1 where dept.department_id=e.department_id and dept.manager_id=e1.employee_id group bydept.department_id,dept.department_name,e1.first_name||e1.last_namehaving count(*)=(select max(count(*)) from employeesgroup by department_id )
4、在这里提醒一下，由于可能出现两个部门人数最多的部门，所以先查出部门人数最多的人数，再去查询部门
