獲取在MySQL查詢正確的行使用AND或

Question

需要從表中獲取特定的行，但查詢返回多行

MYSQL

SELECT DISTINCT 
     id, sender_id, msg, name, profilepic, cur_time, cur_date 
    FROM `chat` 
    WHERE 
     (sender_id = '1' AND receiver_id = '3') 
     OR 
     (sender_id = '3' AND receiver_id = '1') 
     AND 
     chat.id > '3' 

表樣本：

id | sender_id | receiver_id | msg | name | profilepic 
1  1    3  hi Jay  o.jpg 
2  1    3  hey Jay  o.jpg 
3  3    1  hi Tom  o.jpg 
4  1    3  Yes Jay  o.jpg 

的我期望從查詢中得到的第四個ID爲「4」，但查詢不斷返回其他幾行

Answer 1

OR比AND較低的優先級排又一排，所以圍繞在你OR表達圓括號：

WHERE (
    (sender_id = '1' AND receiver_id = '3') 
    OR (sender_id = '3' AND receiver_id = '1') 
) 
    and chat.id > '3' 

---

考慮原WHERE條款：

WHERE 
    (sender_id = '1' AND receiver_id = '3') 
    OR 
    (sender_id = '3' AND receiver_id = '1') 
    AND 
    chat.id > '3' 

因爲AND優先OR，它將被解釋如下：

(sender_id = '1' AND receiver_id = '3') 

    OR 

    ((sender_id = '3' and receiver_id = '1') AND chat.id > '3') 

我的回答將迫使提出的括號兩個OR表達式一起評估，如下所示：

((sender_id = '1' AND receiver_id = '3') OR (sender_id = '3' and receiver_id = '1')) 

    AND 

    chat.id > '3' 

Answer 2

試試這個

SELECT DISTINCT id, sender_id, msg, name, profilepic, cur_time, cur_date FROM `chat` WHERE ((
sender_id = '1' AND receiver_id = '3') OR (sender_id = '3' AND receiver_id = '1')) and chat.id > '3' 

原始查詢匹配具有

sender_id = '1' AND receiver_id = '3' 

，並具有

sender_id = '3' AND receiver_id = '1' AND chat.id > '3 

Answer 3

問題是你試圖在同一時間來評估這兩個條款：

(sender_id = '3' AND receiver_id = '1') 
AND 
chat.id > '3' 

這將永遠是正確的，必須記住，該與運營商綁定比OR-運營商強大

所以只需添加paranthesis圍繞你的兩個ORs，這應該很好

Answer 4

所有你需要做的就是添加paranthesis OR條件操作數。

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