写成这种结构更容易看懂吧
SELECT e.dept_no, e.emp_no, maxSalary FROM dept_emp e, salaries s,(SELECT dept_no, max(salary) maxSalary FROM dept_emp e INNER JOIN salaries s ON e.emp_no = s.emp_no GROUP BY dept_no) t WHERE e.emp_no = s.emp_no and e.dept_no = t.dept_no and s.salary = maxSalary ORDER BY e.dept_no;