Question

I have a couple tables that look like this:

 ___________    ___________
| Books     |  | Tags      |
|-----------|  |-----------|
| book_id   |  | tag_id    |
| book_name |  | tag_name  |
 -----------    ----------- 

And a join table that connects the “many-to-many relationship”:

 ___________
| Books/Tags|
|-----------|
| book_id   |
| tag_id    |
 -----------

I have the following query:

SELECT book_name, tag_name FROM books 
JOIN books_tags ON books.book_id = books_tags.book_id 
JOIN tags ON tags.tag_id = books_tags.tag_id 
WHERE books.book_id = 283

And the following (for books that aren’t tagged):

SELECT book_name FROM books WHERE books.book_id = 283

Is there a way to merge those two queries into one?

Answer 1

You want a LEFT join

SELECT book_name, 
       tag_name 
FROM   books 
       LEFT JOIN books_tags 
         ON books.book_id = books_tags.book_id 
       LEFT JOIN tags 
         ON tags.tag_id = books_tags.tag_id 
WHERE  books.book_id = 283