select d.dept_no, d.dept_name, a.sumfrom departments djoin ( SELECT de.dept_no, count(s.emp_no) as sum from dept_emp de inner join salaries s on de.emp_no = s.emp_no group by de.dept_no) aon d.dept_no = a.dept_no -- 先把2,3表联立,根据薪水表的员工记录数,对应工资数,按部门编号分组。 SELECT de.dept_no, count(s.emp...