Question

我正在处理查询并且非常困难。我将它提炼到下面的内容。

我从feed中获取数据，其中user_id不是当前用户，这种情况是1，隐私设置小于2.我怎么想检查当前用户是否曾回复过，换句话说，prfor表中没有该行的当前用户的行。

此时我的逻辑已经消失了，我无法理解它应该如何运作。它是否需要一个子查询来处理这类事情，还是可以加入呢？

在最后的查询中，还有两个JOIN，但这似乎不会对下面的内容产生影响。

SELECT
   pf.id, 
   pf.privacy
FROM 
   feed pf
WHERE 
   (
      pf.user_id != 1 
      AND pf.privacy < 2
   ) 
   AND NOT (
      SELECT 
         pd.p_for 
      FROM 
         prfor pd 
      WHERE 
         pd.user_id = 1 
         AND pd.pfeed_id = pf.id 
         AND pd.p_for = 1 LIMIT 1
   )

感谢您提供的任何见解。

Answer 1

您必须使用NOT EXISTS：

SELECT pf.id, pf.privacy
FROM feed pf
WHERE (pf.user_id != 1 AND pf.privacy < 2) AND 
     NOT EXISTS (SELECT pd.p_for 
                 FROM prfor pd 
                 WHERE pd.pfeed_id = pf.id AND pd.user_id = 1 AND 
                       pd.p_for = 1)

Answer 2

如果pf.id不在prfor

，你应该使用或不用于测试

    SELECT
    pf.id, pf.privacy
    FROM feed pf
    WHERE (pf.user_id != 1 AND pf.privacy < 2) AND  pf.user_id  NOT IN 
    (SELECT pf.id FROM prfor pd WHERE pd.user_id = 1 AND pd.pfeed_id = pf.id AND pd.p_for = 1 LIMIT 1)

或不存在

    You should use or not in  
    SELECT
    pf.id, pf.privacy
    FROM feed pf
    WHERE (pf.user_id != 1 AND pf.privacy < 2) AND   NOT EXIST
    (SELECT pd.p_for FROM prfor pd WHERE pd.user_id = 1 AND pd.pfeed_id = pf.id AND pd.p_for = 1 LIMIT 1)

Answer 3

SELECT 
topt.* 
FROM fields_options AS topt
WHERE (topt.field_id=2)  AND topt.translation_of  
NOT IN  (SELECT top.translation_of FROM fields_options AS top WHERE top.field_id=2 AND top.translation_lang='ar' ) 
ORDER BY topt.translation_of

MySQL不在子查询中

3 个答案: