Question

I have a books , users and a books_users table.

Now, i want to get a book that is managed by me (user_id = 3) and other user(user_id = 18):

SELECT *
FROM books as Book
LEFT JOIN books_users as BookUser
    ON BookUser.book_id = Book.id
WHERE
    Book.user_count = 2 AND
    BookUser.user_id = 3 AND
    BookUser.user_id = 18

Problem:
as the left join splits the result of books in rows, it doesn’t give a row with the two users…

Answer 1

I believe you want to join to the BookUser table twice to get both conditions and use DISTINCT to get the book once:

SELECT DISTINCT Book.*
FROM books as Book
LEFT JOIN books_users as BookUser1
    ON BookUser.book_id = Book.id
LEFT JOIN books_users as BookUser2
    ON BookUser.book_id = Book.id
WHERE
    Book.user_count = 2 AND
    BookUser1.user_id = 3 AND
    BookUser2.user_id = 18