查找所有员工入职时候的薪水情况

联表查询：分组筛选

SELECT 
  e.emp_no,
  MIN(s.salary) 
FROM
  employees e 
  INNER JOIN salaries s 
    ON e.emp_no = s.emp_no 
GROUP BY e.emp_no 
ORDER BY e.emp_no DESC

或者

SELECT 
  e.emp_no,
  s.salary 
FROM
  employees e 
  INNER JOIN salaries s 
    ON e.emp_no = s.emp_no 
GROUP BY e.emp_no HAVING MIN(s.from_date)
ORDER BY e.emp_no DESC

联表查询：hire_date和dorm_date对应

SELECT 
  e.emp_no,
  s.salary 
FROM
  employees e 
  INNER JOIN salaries s 
    ON e.emp_no = s.emp_no 
WHERE e.hire_date=s.from_date
order by e.emp_no desc