Question

我有3张表如下

表A - 用户回答

 user id    |   question id |   answer option id    |
   1        |           1   |               2       |
   1        |           2   |               1       |

表B - 问题

question id | question text     |
1           | Question 1        |
2           | Question 2        |

表C - 答案

answer id   |   question id |   answer option id    |answer text                |
1           |   1           |                   1   |Question 1 answer 1        |
2           |   1           |                   2   |Question 1  answer 2       |
2           |   2           |                   1   |Question 2 answer 1        |
3           |   2           |                   2   |Question 2  answer 2       |

我想找出哪个用户给出了哪个答案结果应如下所示

    1       |   Question 1  |   Question 1 answer 2     |
    1       |   Question 2  |   Question 2 answer 1     |

我试过了

SELECT * FROM A
LEFT JOIN B ON A.question_id = B.question_id
LEFT JOIN C ON A.answer_option_id = C.answer_option_id

这里有人可以帮助我吗？

Answer 1

您缺少确保最后一次加入能够获得正确问题的答案。

试试这个：

SELECT * FROM A 
LEFT JOIN B ON A.question_id = B.question_id
LEFT JOIN C ON A.answer_option_id = C.answer_option_id AND A.question_id = C.question_id

Answer 2

你需要通过questionid添加group，否则它将在answer表中为每个返回4行。

Warning message: running command ... had status 127

输出：

select a.userid, b.Qtext, c.Atext from answered a 
join quest b on a.qid=b.qid 
left join answer c on a.optid=c.optid and a.qid=b.qid  group by a.qid;

左连接三个表

2 个答案: