我想在MySQL中加入五个表

Question

图书

• bookid（PK）
• 标题
• 价钱

作者

• 撰写（PK）
• AUTHORNAME

出版者

• 耻骨（PK）
• pubname

bookauthors

• bookid（FK）
• AUTHORID

bookpublisher

• bookid（FK）
• 发布商ID

我想加入所有五个表并获取这些列值：

• BOOKID
• 标题
• 价钱
• AUTHORNAME
• pubname

我应该只获得一行查询以获得上述结果。 我写的是：

select books.*, authors.authorname
from authors,books
inner join bookauthors on books.bookid = bookauthors.bookid
inner join publisherbook on books.bookid = publisherbook.bookid
where books.bookid = 459567;

但相反，我得到了许多重复数据的行。

Answer 1

您需要为所有表使用连接。 在FROM子句中使用多个表会生成笛卡尔积。 试试这个

SELECT books.bookid, books.title, books.price, authors.authorname
FROM books
INNER JOIN bookauthors ON books.bookid = bookauthors.bookid
INNER JOIN publisherbook ON books.bookid = publisherbook.bookid
INNER JOIN authors ON bookauthors.authorid = authors.authorid -- assuming you meant authorid and not authored
WHERE books.bookid = 459567;

当然，如果您的书有多个作者，您将在结果集中获得多行。

我不确定你为什么要加入publisherbook （或原始列表中的bookpublisher ），除非你只是确保你的图书有出版商。 同样，多个发布商将产生更多（重复）结果。

如果您只是想确保您的图书至少有一个发布商，请尝试相应...

SELECT books.bookid, books.title, books.price, authors.authorname
FROM books
INNER JOIN bookauthors ON books.bookid = bookauthors.bookid
INNER JOIN authors ON bookauthors.authorid = authors.authorid -- assuming you meant authorid and not authored
WHERE EXISTS (
    SELECT 1 FROM publisherbook
    WHERE publisherbook.bookid = books.bookid
) AND books.bookid = 459567;