Php 在mysql中连接两个表，返回不相关的行

我有两张桌子：

表1：问题id、问题、日期

表2：答案id、问题id、答案、日期

一个问题可以有多个答案，有些问题没有答案。我只想输出未回答的问题

类似于SELECT*FROMQUOTES、ANSWERESWHERE QUOTES.id的查询=answers.question\u id按问题分组。id不起作用

有人能帮我这样的新手吗？我对mysql的东西太迷恋了

SELECT id, question, date
FROM questions q 
WHERE NOT EXISTS
    (SELECT * FROM answers a 
     WHERE a.question_id = q.id)

或

或

从中选择* 问题、答案

---

其中answers.answer=null或answers.answer=

多谢各位。没想到会这么快。再次感谢你，它起作用了。爱mysql

SELECT id, question, date
FROM questions q 
LEFT JOIN answers a ON a.question_id = q.id
WHERE a.id IS NULL

SELECT id, question, date
FROM questions q 
WHERE q.id NOT IN 
    (SELECT question_id FROM answers WHERE question_id IS NOT NULL)
                                 /* If question_id can't be NULL this is not needed*/

SELECT Q.id, Q.question, Q.date
FROM questions Q LEFT JOIN answers A ON (Q.id = A.question_id)
WHERE A.id IS NULL