MySQL：從多個表中選擇數據，其中有多個“多對多”關系表

Question

有五個表如下

請參考這個 db-fiddle https://www.db-fiddle.com/f/c7mYgFSQUFhCbUoEvpAzpM/0

圖書

• book_id (PK)
• 書名

作者

• author_id (PK)
• 作者姓名

類別

• cat_id (PK)
• 貓名

（其中表Authors和Category通過多對多關系連接到Books ）

書作者

• bookauthor_id (PK)
• book_id (FK)
• author_id (FK)

圖書分類

• bookcat_id
• book_id (FK)
• cat_id (PK)

對於給定的 book_id，我想查詢並獲取 book_name、author_name、cat_name。

我怎樣才能在mysql中實現這一點？

Answer 1

您可以使用以下查詢

 SELECT b.book_name, a.author_name, c.cat_name
 FROM Books b
 JOIN BookAuthor ba ON b.book_id =ba.book_id
 JOIN Authors a ON a.author_id = ba.author_id
 JOIN BookCategory bc ON bc.book_id =b.book_id 
 JOIN Categories c ON bc.cat_id = c.cat_name
 WHERE b.book_id = 101 -- specify book id 

Answer 2

你可能想要：

SELECT b.title, ba.authors, bc.categories
FROM books b LEFT  JOIN
     (SELECT ba.book_id, GROUP_CONCAT(a.name) as authors
      FROM bookauthor ba JOIN
           authors a
           ON a.auth_id = ba.auth_id
      GROUP BY ba.book_id
     ) ba
     ON b.book_id = ba.book_id LEFT JOIN
     (SELECT bc.book_id, GROUP_CONCAT(c.name) as categories
      FROM bookcategory bc JOIN
           categories c
           ON bc.cat_id = c.cat_id
      GROUP BY bc.book_id
     ) bc
     ON bc.book_id = b.book_id 
WHERE b.book_id = 101 -- specify book id 
GROUP BY b.book_id, b.title;

這是一個 db<>fiddle。