具有多个联接的 SQL 分组错误地组合结果

Question

您好，我的查询在不应该合并记录时遇到了问题。

我有两个表 Authors 和 Publications，它们通过出版物 ID 以多对多关系相关。由于每个作者可以有许多出版物，并且每个出版物有许多作者。我希望我的查询返回一组作者的每一篇出版物，并包括对分组到一个字段中的出版物做出贡献的每个其他作者的 ID。 （我正在使用 mySQL）

我尝试在下面以图形方式描绘它

    Table: authors               Table:publications
AuthorID | PublicationID        PublicationID | PublicationName
    1    |   123                       123    |       A
    1    |   456                       456    |       B
    2    |   123                       789    |       C
    2    |   789
    3    |   123
    3    |   456

我希望我的结果集如下

 AuthorID | PublicationID | PublicationName | AllAuthors
     1    |       123     |        A        |    1,2,3
     1    |       456     |        B        |    1,3
     2    |       123     |        A        |    1,2,3
     2    |       789     |        C        |     2
     3    |       123     |        A        |    1,2,3
     3    |       456     |        B        |    1,3

这是我的查询

Select   Author1.AuthorID,
    Publications.PublicationID,
    Publications.PubName,
    GROUP_CONCAT(TRIM(Author2.AuthorID)ORDER BY Author2.AuthorID ASC)AS 'AuthorsAll'
FROM Authors AS Author1
LEFT JOIN Authors AS Author2
ON Author1.PublicationID = Author2.PublicationID
INNER JOIN Publications
ON Author1.PublicationID = Publications.PublicationID
WHERE Author1.AuthorID ="1" OR Author1.AuthorID ="2" OR Author1.AuthorID ="3" 
GROUP BY Author2.PublicationID

但它返回以下内容

 AuthorID | PublicationID | PublicationName | AllAuthors
     1    |       123     |        A        |    1,1,1,2,2,2,3,3,3
     1    |       456     |        B        |    1,1,3,3
     2    |       789     |        C        |     2

当 where 语句中只有一个 AuhorID 时，它确实提供了所需的输出。 我一直无法弄清楚，有谁知道我哪里出错了？

Answer 1

要消除重复作者，请将：更改

ON Author1.PublicationID = Author2.PublicationID

为：

ON Author1.PublicationID = Author2.PublicationID AND
   Author1.AuthorID <> Author2.AuthorID

另外，将：更改

GROUP BY Author2.PublicationID

为：

GROUP BY Author1.AuthorID, Author2.PublicationID

Answer 2

我想我不确定为什么你首先需要 GROUP BY 。为什么不能像这样使用相关子查询：

Select   Author1.AuthorID
    ,  Publications.PublicationID
    , Publications.PubName
    , (
        Select GROUP_CONCAT(TRIM(Author2.AuthorID) ORDER BY Author2.AuthorID ASC) 
        From Authors As Author2
        Where Author2.PublicationID = Publications.PublicationID
        ) AS 'AuthorsAll'
FROM Authors AS Author1
    INNER JOIN Publications
        ON Author1.PublicationID = Publications.PublicationID
Where Author1.AuthorId In("1","2","3")