mysql - 如何编写条件明智的结果提供查询？

Question

嗨，我想编写一个 mysql 查询，给出一个条件明智的结果。

例如。我有一个包含问题、答案值、用户选择值字段的表。

用户可以参加多次回答该问题。

qid righttanz wronganz
11 4 2
11 4 4
11 4 1
25 1 1

我想像这样
qid righttanz wronganz
11 1 2   
25 1 0   

我想显示用户对该问题提供正确和错误答案的次数？我怎样才能为此编写一个mysql查询？任何机构都可以帮助我吗？

Answer 1

SELECT SUM(IF(answer = 42, 1, 0)) AS correct_count, count(*) as total_count
FROM answers
WHERE user_id = 13

假设user_id您要检查的是 13，正确答案是 42

Answer 2

对于所有问题

SELECT a.userId, q.qid
,SUM( CASE WHEN q.answer = a.answer THEN 1 ELSE 0 END) AS correct_answers
,SUM( CASE WHEN q.answer = a.answer THEN 0 ELSE 1 END) AS wrong_answers
FROM questions q
JOIN answers a ON q.qid = a.qid
GROUP BY a.userId, q.qid

对于一个特定的问题

SELECT a.userId
,SUM( CASE WHEN q.answer = a.answer THEN 1 ELSE 0 END) AS correct_answers
,SUM( CASE WHEN q.answer = a.answer THEN 0 ELSE 1 END) AS wrong_answers
FROM questions q
JOIN answers a ON q.qid = a.qid
WHERE q.qid = <question_id>
GROUP BY a.userId