如何寫條件明智的結果提供查詢？

Question

嗨我想編寫一個mysql查詢，給出一個條件明智的結果。例如

。我有一個問題，答案值，用戶選擇值字段的表。

用戶可以參加多次回答該問題。

 
qid  rightanz  wronganz 
11   4    2 
11   4    4 
11   4    1 
25   1    1 

I want out put like this 
qid  rightanz  wronganz 
11   1   2 
25   1   0 

我想顯示多少次的用戶提供了這個問題，正確和錯誤的答案？ 我該如何寫一個mysql查詢呢？任何機構都可以幫助我？

Answer 1

對於所有問題

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 

對於一個具體的問題

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 

Answer 2

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

假設user_id要檢查是13，正確答案是42