SQL查詢 - 使用AND

Question

下面的查詢不返回任何結果

SELECT user_id FROM test WHERE poll_id = 2 AND (question_id = 2 AND answer_id = 5) AND (question_id = 3 AND answer_id = 8); 

這是正確的語法或沒有？

表數據是

|poll_id | question_id | answer_id | user_id | 
|--------|-------------|-----------|---------| 
| 2  | 2   | 5  | 2  | 
| 2  | 3   | 8  | 2  | 

結果應該是2

Answer 1

它不會因爲你的where子句不匹配

AND條件，您應將其更改爲：

SELECT user_id FROM test WHERE poll_id = 2 
AND 
((question_id = 2 AND answer_id = 5) 
OR (question_id = 3 AND answer_id = 8)); 

UPDATE

SELECT t.user_id FROM test t WHERE poll_id = 2 
AND exists ( select 1 from test where 
(question_id = 2 AND answer_id = 5 and user_id=t.user_id)) 
AND question_id = 3 AND answer_id = 8 

Answer 2

您需要使用至少一個或與組或運算部分，以防止任何precendence錯誤：

SELECT user_id FROM test WHERE poll_d = 2 
    AND ((question_id = 2 AND answer_id = 5) 
     OR (question_id = 3 AND answer_id = 8)); 

這意味着：所有具有poll_d = 2和question_id = 2 AND answer_id = 5或question_id = 3 AND answer_id = 8（技術上使用OR）的條目將意味着「至少一個......「，但在你的情況下，沒有辦法使一行匹配兩個條件）。

你的查詢可以被理解爲具有poll_d = 2和所有條目都，question_id = 2 AND answer_id = 5和question_id = 3 AND answer_id = 8（這是不可能的，因此查詢沒有結果）。

請注意，在這種情況下您會得到2個結果。如果你想只有一個，使用distinct關鍵字：SELECT distinct(user_id) FROM ...

Answer 3

您在布爾邏輯這裏有些困難。另外，你可能有一個錯字在第一條件（poll_d） 什麼你可能想要的是

SELECT user_id FROM test WHERE poll_id = 2 AND 
((question_id = 2 AND answer_id = 5) OR (question_id = 3 AND answer_id = 8)); 

在查詢括號並不在所有問題，因此它可以被翻譯爲

SELECT user_id FROM test WHERE poll_id = 2 
AND question_id = 2 AND answer_id = 5 
AND question_id = 3 AND answer_id = 8; 

question_id = 2 AND question_id = 3根據布爾邏輯和理智是False。同樣確實爲answer_id = 5 AND answer_id = 8

Answer 4

SELECT user_id FROM test WHERE poll_d = 2 
AND ((question_id = 2 AND answer_id = 5) 
OR (question_id = 3 AND answer_id = 8)); 

Answer 5

使用DISTINCT SQL方法試試。

SELECT DISTINCT(user_id) FROM test WHERE poll_d = 2 
AND ((question_id = 2 AND answer_id = 5) 
OR (question_id = 3 AND answer_id = 8)); 

而你的布爾邏輯，我用了OR。

PS：未經測試。

Answer 6

在上一個條件中將AND更改爲OR。

SELECT 
    user_id FROM test 
WHERE poll_d = 2 
AND (question_id = 2 AND answer_id = 5) 
OR (question_id = 3 AND answer_id = 8); 

Answer 7

括號在你的where語句沒有效果。 你寫過 question_id = 3 AND question_id = 2, 當然它不會返回任何結果！ 也許你需要像這樣

SELECT user_id FROM test WHERE poll_d = 2 AND ((question_id = 2 AND answer_id = 5) OR (question_id = 3 AND answer_id = 8)) 

Answer 8

嘗試。

SELECT user_id FROM test WHERE poll_d = 2 
AND ((question_id = 2 AND answer_id = 5) 
OR (question_id = 3 AND answer_id = 8)); 

它給0記錄的原因是因爲過濾器（WHERE條件）實際上應用於單行。該查詢的工作原理如何將您的過濾器與每一行相匹配。

Answer 9

你需要加入兩個記錄，因此：

select p1.user_id from poll p1, poll p2 
where p1.poll_id = 2 and p2.poll_id = 2 and 
p1.question_id = 2 and p1.answer_id = 5 and 
p2.question_id = 3 and p2.answer_id = 8 and 
p1.user_id = p2.user_id