mysql - 也有 'null' 导致查询

Question

这是存储我的数据的 3 个表:

答案

answer_id | question_id | answer

问题

question_id | question

users_answers

user_answer_id | answer_id | question_id

我在实践中必须做的事情:

对于给定的问题，收集所有 的答案并计算例如有多少人回答了 A 或 B。这里的重点是我需要所有答案，即使没有人选择它作为可能的好答案。

这是我的查询:

SELECT   q.question_id,
         q.question,
         a.answer_id,
         a.answer
FROM     questions AS q
    JOIN answers AS a ON
         q.question_id = a.question_id
    JOIN users_answers ON
         a.answer_id = users_answers.answer_id
WHERE q.question_id = 19

这是我的实际结果(有例子):

question_id    |    question    |    answer_id    |    answer

     19             'blabla'             12           'C blabla'
     19             'blabla'             12           'C blabla'
     19             'blabla'             10           'A blabla'
     19             'blabla'             13           'D blabla'

没有用户给出“B blabla”作为可能的好答案，但我的结果中仍然需要这个结果。

我该怎么做？

非常感谢

Answer 1

SELECT questions.question_id, 
       questions.question, 
       answers.answer_id, 
       answers.answer, 
       (SELECT Count(users_answers.user_answer_id) 
        FROM   users_answers 
        WHERE  users_answers.question_id = 1 
               AND users_answers.answer_id IN ( 1, 2 )) AS 
       total_people_answered_anserA_B 
FROM   users_answers 
       INNER JOIN questions 
               ON questions.question_id = users_answers.question_id 
       INNER JOIN answers 
               ON answers.answer_id = users_answers.answer_id 
WHERE  users_answers.question_id = 1;