MySQL

Question

我有一个 table 的结构类似于下面提到的格式。他们看起来像这样

本书

| ID | Title |
| 1  | A     |
| 2  | B     |

Book_Collaborators

| COLLAB_ID |BookID | Type      |
| 1         | 1     | Author    |
| 2         | 1     | Editor    |
| 3         | 1     | Publisher |

合作者

| ID | Title |
| -- | ----- |
| 1  | D     |
| 2  | E     |
| 3  | F     |

我需要以下格式的结果，其中作者、编辑和出版商等详细信息显示在不同的列中。

请注意，有时 Book_Collaborators table

中可能没有详细信息

| BOOK ID   | Title  | Author | Editor | Publisher |
| --------- | -----  |------  | ------ | --------- | 
| 1         | A      | D      | E      | F         |

我想出了这个查询，但我不想多次加入同一个 table

select book.id as BookId, c.title as Author,c1.title as Editor
from Book book
left join Book_Collaborators bc on (book.id=bc.book_id and bc.type='Author')
left join Collaborators c on (bc.COLLAB_ID=c.id)
left join Book_Collaborators bc1 on (book.id=bc1.book_id and bc1.type='Editor')
left join Collaborators c1 on (bc1.COLLAB_ID=c1.id)

Answer 1

显示所有图书信息，无论是否在 book_collaborator table 中具有相关值。如果只需要相关值，则使用 INNER JOIN 而不是 LEFT JOIN。由于图书ID在图书中是唯一的table，因此在标题列使用聚合函数以避免它添加GROUP BY子句。

-- MySQL
SELECT b.id BOOK_ID
     , MAX(b.title) Title
     , MAX(CASE WHEN bc.btype = 'Author' THEN c.title END) Author
     , MAX(CASE WHEN bc.btype = 'Editor' THEN c.title END) Editor
     , MAX(CASE WHEN bc.btype = 'Publisher' THEN c.title END) Publisher
FROM Book b
LEFT JOIN Book_Collaborators bc
       ON b.id = bc.book_id
LEFT JOIN Collaborators c
       ON c.id = bc.collab_id
GROUP BY b.id

请从urlhttps://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=069dc205f176968d61d462ad3cad7568

检查

MySQL - 一对多查询，结果在单独的列中

MySQL - One to Many Query with results in separate columns

database

one-to-many