加入MySQL中2個表，返回不相關

Question

我有2個表中的行：

表1：問題（ID，問題，日期）

表2：答案（ID，question_id，答案，日期）

一個問題可以有1個以上的答案，有些問題沒有答案。我想只輸出懸而未決的問題

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

有人能幫助新手喜歡我，我很迷失在這一切MySQL的東西。

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 問題，答案 WHERE answers.answer = null或answers.answer = 「」;