题目链接：​​点击打开链接​​

题目大意：略。

解题思路：略。

AC 代码

-- 解决方案(1)
SELECT
  id,
  `name`
FROM
  Students AS s
WHERE NOT EXISTS(
  SELECT
    1
  FROM
    Departments
  WHERE
    id = s.department_id
);

-- 解决方案(2)
SELECT id, name 
FROM Students
WHERE department_id NOT IN (SELECT id FROM Departments)