题解 | 在子查询中使用窗口函数，计算每组工资排序rk

SELECT
    dept_no,
    emp_no,
    salary AS maxSalary
FROM(
    SELECT 
        de.emp_no, de.dept_no, s.salary,
        RANK() OVER(PARTITION BY dept_no ORDER BY salary DESC) AS rk
    FROM dept_emp de
    JOIN salaries s USING(emp_no)
) t1
WHERE rk=1
ORDER BY dept_no