mysql - SQL 缺少记录问题

Question

大家好，对于这个愚蠢的问题，我深表歉意，但我遇到了一个问题，希望你们能给我指出正确的方向——请耐心等待，我是一个完全的初学者。我设置了三个表，大致如下所示:

table 1 quizquestions
Question ID, etc.
Int

table 2 quizanswers
AnswerID, QuestionID,correct Answer
Int         Int         Bool

table 3 useranswers
UserAnswerID, AnswerID, QuestionID
Int                Int         Int

我的问题是当我运行这样的查询时:

SELECT A.AnswerID AS Answer, UA.AnswerID AS UserAnswer 
FROM quizanswers AS A, useranswers UA 
WHERE A.CorrectAnswer = TRUE 
  AND UA.QuestionID 
  AND  A.QuestionID = X

查询将返回如下结果:

Answer UserAnswer 
  1        1

如果quizanswers 和useranswers 表中都有记录，查询将成功返回结果。但是，问题是当 useranswers 表中没有记录时，不会返回任何结果。如果上面的代码不够清晰，我深表歉意，在此先感谢您。

Answer 1

我不确定我是否理解问题背后的商业案例，但这会为您提供测验答案的记录，即使用户答案中没有相应的记录也是如此:

    SELECT A.AnswerID AS Answer, UA.AnswerID AS UserAnswer FROM quizanswers AS A LEFT JOIN useranswers UA ON UA.QuestionID = A.QuestionD WHERE A.CorrectAnswer = TRUE AND A.QuestionID = X