目標：想要顯示書籍、書籍喜歡計數、作者和作者喜歡計數。
-- books: start
SELECT * FROM books
-- likes: get like count of books
JOIN likes ON likes.id = books.likes_id
-- merge table: join to book
JOIN authors_books ON books.id = authors_books.book_id
-- authors: join merge table
JOIN authors ON authors.id = authors_books.author_id
-- likes: get like count of authors
JOIN ????????
我被作者喜歡所困。而不是 likes_id：我想要 likes_count（請參閱 RESULTS GRID 影像）。
我試過了：
加入喜歡 AS l2 ON likes.id = authors.likes_id
沒有運氣。在頂部顯示所有正確的列資訊，但輸出為空白。
uj5u.com熱心網友回復：
你必須加入likes兩次，一次是為了書，一次是為了作者。
由于您使用同一張表加入，因此您需要給它們起別名以區分它們。
SELECT books.id, books.title, books.pages, book_likes.count AS book_likes,
authors.first_name, author.last_name, author_likes.count AS author_likes
FROM books
JOIN likes AS book_likes ON book_likes.id = books.likes_id
JOIN authors_books ON books.id = authors_books.book_id
JOIN authors ON authors.id = authors_books.author_id
JOIN likes AS author_likes ON author_likes.id = authors.likes_id
轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/427359.html
標籤：mysql
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