三种方法

方法一：获取salaries中from_data中最小的对应的salary和emp_no，因为salaries可能涨薪，所以这张表一个员工可能有多条记录。

SELECT
    emp_no,
    salary 
FROM
    salaries 
GROUP BY
    emp_no 
HAVING
    min( from_date ) 
ORDER BY
    emp_no DESC

方法二：hire_data时间和from_data时间一致

SELECT
    e.emp_no,
    s.salary 
FROM
    employees AS e
    INNER JOIN salaries AS s ON e.emp_no = s.emp_no 
    AND e.hire_date = s.from_date 
ORDER BY
    e.emp_no DESC

方法三：hire_data时间和from_data时间一致

SELECT
    e.emp_no,
    s.salary 
FROM
    employees AS e,
    salaries AS s 
WHERE
    e.emp_no = s.emp_no 
    AND e.hire_date = s.from_date 
ORDER BY
    e.emp_no DESC