加入MySQL中2个表，返回不相关

Question

我有2个表中的行：

表1：问题（ID，问题，日期）

表2：答案（ID，question_id，答案，日期）

一个问题可以有1个以上的答案，有些问题没有答案。我想只输出悬而未决的问题

像SELECT * FROM问题,答案查询WHERE questions.id!=answers.question_id group by questions.id不起作用

有人能帮助新手喜欢我，我很迷失在这一切MySQL的东西。

Answer 1

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

OR

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

OR

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*/ 

Answer 2

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 

Answer 3

SELECT * FROM 问题，答案 WHERE answers.answer = null或answers.answer = “”;