Question

我在使用SQL查询时遇到了一些麻烦。以下查询返回权限结果。它返回表中的成员，这些成员是男性，说瑞典语并且属于第4组。

SELECT DISTINCT Member.ID 
FROM Member
LEFT OUTER JOIN Experience ON Experience.MemberID = Member.ID
LEFT OUTER JOIN Qualification ON Qualification.MemberID = Member.ID
LEFT OUTER JOIN Language On Language.MemberID = Member.ID
LEFT OUTER JOIN Member_Interests ON Member_Interests.MemberID = Member.ID
LEFT OUTER JOIN Group_Members ON Group_Members.MemberID = Member.ID
WHERE 1=1 AND Gender = 'male' AND Language.Name IN ( 'Swedish' ) AND Group_Members.GroupID = 4

但是，如果我排除另一个直接在成员表上搜索的条件，那么简单地忽略language.Name。即

SELECT DISTINCT Member.ID 
FROM Member
LEFT OUTER JOIN Experience ON Experience.MemberID = Member.ID
LEFT OUTER JOIN Qualification ON Qualification.MemberID = Member.ID
LEFT OUTER JOIN Language On Language.MemberID = Member.ID
LEFT OUTER JOIN Member_Interests ON Member_Interests.MemberID = Member.ID
LEFT OUTER JOIN Group_Members ON Group_Members.MemberID = Member.ID
WHERE 1=1 AND Language.Name IN ( 'Swedish' ) AND Group_Members.GroupID = 4

上述查询返回组4中的所有成员。瑞典语部分被忽略，只要Langauges表中有一个名为Swedish的语言，就会返回所有用户。如果表中没有该语言，则不会返回任何用户。

我希望第二个查询只返回第4组中讲瑞典语的所有成员。有谁知道为什么没有发生这种情况？

Answer 1

将左连接表上的过滤器移动到连接。

例如：

LEFT OUTER JOIN Language On Language.MemberID = Member.ID 
     and LanguageID in ('Swedish')
LEFT OUTER JOIN Group_Members ON Group_Members.MemberID = Member.ID 
     AND Group_Members.GroupID = 4 
...
WHERE 1=1 AND Gender = 'male'

等

Answer 2

你尝试过内连接吗？

或只是

SELECT DISTINCT Member.ID 
FROM Member, Language
LEFT OUTER JOIN Experience ON Experience.MemberID = Member.ID
LEFT OUTER JOIN Qualification ON Qualification.MemberID = Member.ID
LEFT OUTER JOIN Member_Interests ON Member_Interests.MemberID = Member.ID
LEFT OUTER JOIN Group_Members ON Group_Members.MemberID = Member.ID
WHERE 1=1 AND Gender = 'male' AND Language.MemberID = Member.ID AND Language.Name IN ( 'Swedish' ) AND Group_Members.GroupID = 4

Answer 3

澄清：你最终想要什么，因为LEFT JOIN意味着无论左侧表和WHERE条件是什么，但即使右侧表上没有任何东西也要抓住。将右侧表添加到where时，它实际上创建为内部联接。你是否只想要明确的男性，语言瑞典语和第4组？如果是这样，我会做普通连接

SELECT DISTINCT 
      M.ID 
   FROM Member M
      LEFT OUTER JOIN Experience E
         ON M.ID = E.MemberID 
      LEFT OUTER JOIN Qualification Q
         ON M.ID = Q.MemberID 
      LEFT OUTER JOIN Language L 
         ON M.ID = L.MemberID 
      LEFT OUTER JOIN Member_Interests MI
         ON M.ID = MI.MemberID 
      LEFT OUTER JOIN Group_Members GM
         ON M.ID = GM.MemberID 
   WHERE 
          1=1 
      AND M.Gender = 'male' 
      AND L.Name IN ( 'Swedish' ) 
      AND GM.GroupID = 4

实际上从LEFT JOIN更改为INNER JOIN仅获取性别为男性，语言为瑞典语且组为4的记录。为了更好地理解和交换查询，我展示了以下内容：

SELECT DISTINCT 
      M.ID 
   FROM Member M
      JOIN Language L 
         ON M.ID = L.MemberID 
         AND L.Name IN ('Swedish')
      JOIN Group_Members GM
         ON M.ID = GM.MemberID 
        AND GM.GroupID = 4
   WHERE 
          1=1 
      AND M.Gender = 'male'

我删除了其他LEFT JOIN条目，因为它们与返回的不同成员“ID”值的最终请求无关。为什么加入，如果不使用。

Answer 4

如果您之前的查询给出了正确的结果。然后这个必须在你需要时为你工作

SELECT DISTINCT Member.ID 
FROM Member
LEFT OUTER JOIN Experience ON Experience.MemberID = Member.ID
LEFT OUTER JOIN Qualification ON Qualification.MemberID = Member.ID
LEFT OUTER JOIN Language On Language.MemberID = Member.ID
LEFT OUTER JOIN Member_Interests ON Member_Interests.MemberID = Member.ID
LEFT OUTER JOIN Group_Members ON Group_Members.MemberID = Member.ID
WHERE 1=1 AND Gender IN ('male','female') AND Language.Name IN ( 'Swedish' ) 
AND Group_Members.GroupID = 4;

尝试一下，如果有任何问题。评论请，否则享受它：）

左外连接sql中忽略的子句

4 个答案: