令人不安的MySQL加入操作

Question

兩個表格，一個包含問題，另一個包含每個用戶的答案，如果他們已經回答的話。我試圖拉取由權重（最重要）排序的下一個問題，其中用戶a在答案表中沒有答案。

我的表是這樣的：

table: app_questions 
| id  | int(11)  | NO | PRI | NULL | auto_increment | 
| owneruid | int(11)  | YES |  | NULL |    | 
| question | varchar(350) | YES |  | NULL |    | 
| answer_1 | varchar(350) | YES |  | NULL |    | 
| answer_2 | varchar(350) | YES |  | NULL |    | 
| answer_3 | varchar(350) | YES |  | NULL |    | 
| answer_4 | varchar(350) | YES |  | NULL |    | 
| weight | decimal(5,2) | YES |  | NULL |    | 
| datetime | datetime  | YES |  | NULL |    | 

table: app_answers 
| id     | int(11)  | NO | PRI | NULL | auto_increment | 
| uid    | int(11)  | YES |  | NULL |    | 
| quid    | int(11)  | YES |  | NULL |    | 
| answer    | int(11)  | YES |  | NULL |    | 
| importance   | int(11)  | YES |  | NULL |    | 
| answer_status  | varchar(20) | YES |  | NULL |    | 
| answer_explanation | varchar(200) | YES |  | NULL |    | 
| datetime   | datetime  | YES |  | NULL |    | 

我已經嘗試了一些變化，但還沒有得到正是我需要的：

SELECT uid , 
     question , 
     answer_1 , 
     answer_2 , 
     answer_3 , 
     answer_4 , 
     weight , 
     answer_status 
FROM match_questions 
     LEFT JOIN match_answers ON match_questions.id = match_answers.quid 
WHERE answer_status IS NULL 
     AND EXISTS (SELECT * 
        FROM match_answers 
        WHERE uid = 1) 
ORDER BY weight DESC LIMIT 1; 



    SELECT uid , 
     question , 
     answer_1 , 
     answer_2 , 
     answer_3 , 
     answer_4 , 
     weight , 
     answer_status 
FROM match_questions 
     LEFT JOIN match_answers ON match_questions.id = match_answers.quid 
WHERE uid IS NULL 
     AND answer_status IS NULL 
ORDER BY weight DESC LIMIT 1; 




SELECT uid , 
      question , 
      answer_1 , 
      answer_2 , 
      answer_3 , 
      answer_4 , 
      weight , 
      answer_status 
    FROM match_questions 
      LEFT JOIN match_answers ON match_questions.id = match_answers.quid 
    WHERE answer_status IS NULL 
      AND uid IS NULL 
    ORDER BY weight DESC LIMIT 1; 

任何指導讚賞。

Answer 1

這很難說沒有看到樣本數據和期望的輸出，但恕我直言，您的查詢可能是這樣

SELECT q.id, 
     q.question, 
     q.answer_1, 
     q.answer_2, 
     q.answer_3, 
     q.answer_4, 
     q.weight 
    FROM match_questions q LEFT JOIN match_answers a 
    ON q.id = a.quid 
    AND a.uid = 1 
WHERE a.quid IS NULL 
ORDER BY q.weight, q.id 
LIMIT 1 

這裏是SQLFiddle演示