如何連接兩個相同的表一起在MySQL

下面是我的數據庫架構三個表：如何連接兩個相同的表一起在MySQL

-- Table where I store authors 
SELECT author_id, first_name, last_name FROM author; 
╔═══════════╦════════════╦═══════════╗ 
║ author_id ║ first_name ║ last_name ║ 
╠═══════════╬════════════╬═══════════╣ 
║   1 ║  Ernest ║ Hemingway ║ 
║   2 ║  Walt ║ Whitman ║ 
║   3 ║  Mark ║  Twain ║ 
║  ... ║  ... ║  ... ║ 
╚═══════════╩════════════╩═══════════╝ 

-- Junction-table to keep track of books and their respective authors 
SELECT book_id, author_id FROM book_author; 
╔═════════╦═══════════╗ 
║ book_id ║ author_id ║ 
╠═════════╬═══════════╣ 
║  37 ║   1 ║ 
║  37 ║   2 ║ 
║  ... ║  ... ║ 
╚═════════╩═══════════╝ 

-- Temporary table to store, once again, books and their respective authors 
-- but only for updating book purposes. The table is identical in its structure 
-- to the book_author table 
SELECT book_id, author_id FROM temp_book_author; 
╔═════════╦═══════════╗ 
║ book_id ║ author_id ║ 
╠═════════╬═══════════╣ 
║  37 ║   3 ║ 
║  ... ║  ... ║ 
╚═════════╩═══════════╝

現在，我可以用這個查詢樓下得到下面的結果：

SET @BOOK_ID = 37; 
SELECT @BOOK_ID AS book_id, 
     a.last_name, 
     a.first_name 
FROM book_author AS ba 
     LEFT JOIN author AS a 
       ON ba.author_id = a.author_id 
WHERE book_id = @BOOK_ID; 
╔═════════╦════════════╦═══════════╗ 
║ book_id ║ first_name ║ last_name ║ 
╠═════════╬════════════╬═══════════╣ 
║  37 ║  Ernest ║ Hemingway ║ 
║  37 ║  Walt ║ Whitman ║ 
╚═════════╩════════════╩═══════════╝

以下是我想要實現的內容：我需要將與該書相關聯的行（如果存在更多的行）添加到上面的選擇中，該表中的ID爲37，如果你願意，可以製作兩張桌子， ：BOOK_AUTHOR和temp_book_author也就是說，一個表就好像它們是一個表來開始：

╔═════════╦════════════╦═══════════╗ 
║ book_id ║ first_name ║ last_name ║ 
╠═════════╬════════════╬═══════════╣ 
║  37 ║  Ernest ║ Hemingway ║ 
║  37 ║  Walt ║ Whitman ║ 
║  37 ║  Mark ║  Twain ║ 
╚═════════╩════════════╩═══════════╝

我該如何解決這個問題？

來源

2013-04-23 Mikhail

你是否需要'INSERT INTO BOOK_AUTHOR（book_id，author_id）SELECT book_id，Author_id FROm temp_book_author;'或者我誤解了 – Scotch 2013-04-23 04:25:56

@Scotch：請添加它作爲答案，以便它可能被接受。 – 2013-04-23 04:39:17

@RoneyMichael太晚了:) – Scotch 2013-04-23 05:53:47

使用UNION：

SET @BOOK_ID = 37; 
SELECT @BOOK_ID AS book_id, 
     a.last_name, 
     a.first_name 
FROM (SELECT * FROM book_author 
     UNION 
     SELECT * FROM temp_book_author) AS ba 
     LEFT JOIN author AS a 
       ON ba.author_id = a.author_id 
WHERE book_id = @BOOK_ID;

您還可以創建一個表，自動合併兩個表：

CREATE TABLE union_book_author (book_id int, author_id int) 
ENGINE = MERGE 
UNION = (book_author, temp_book_author);

然後，您可以在查詢中使用union_book_author。

來源

2013-04-23 04:45:21 Barmar

我同意Scotch的評論，理想情況下，您應該將temp_book_author中的數據插入book_author，然後從該表中選擇，但如果有理由不想這樣做，那麼您需要使用sql命令'union'。

SET @BOOK_ID = 37; 
SELECT @BOOK_ID AS book_id, a.last_name, a.first_name 
FROM book_author AS ba 
LEFT JOIN author AS a ON ba.author_id = a.author_id 
WHERE book_id = @BOOK_ID 
UNION 
select t.book_id, a1.last_name, a1.firstname 
from temp_book_author as t 
left join author as a1 on t.author_id = a1.author_id 
where t.book_id = @BOOK_ID

來源

2013-04-23 04:45:14

如何連接兩個相同的表一起在MySQL

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