Mysql 带左连接的条件筛选

我有一个

books

、

users

和一个

books\u users

表

现在，我想得到一本由我（user_id=3）和其他用户（user_id=18）管理的书：

问题:

---

由于左联接将书籍的结果拆分为行，因此它不会给出包含两个用户的行…

我相信您希望两次联接到BookUser表以获得这两个条件，并使用DISTINCT获得一次书籍：

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

---

我不知道用户计数列

这就提供了3人或18人使用的书籍

SELECT *
FROM books as Book
INNER JOIN books_users as BookUser
    ON BookUser.book_id = Book.id
WHERE
    Book.user_count = 2 AND
    BookUser.user_id IN  (3,18) 

或

编辑：这提供了3和18都使用的书籍

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

---

BookUser.user_id

怎么可能同时是3岁和18岁？@Andrew这只是他希望它工作的一个例子。我相信他正在寻找一本

书

，它正好有2个

图书用户

s，用户id为

3

和

18

。我不理解左连接和区分的必要性？@nitimidha

左连接

是有争议的，但是

DISTINCT

使它每本书只返回一行，而不是两行。你说得对。我想它仍然会有两行，但这是最初的问题，我们现在已经过了这个阶段。

不同的

是多余的。您的查询将返回不正确的结果。示例：一本书a

user\u id

s

3

和

5

。它有

3或18

和

2

@G-Nugget的用户计数，我被一个变量有两个值弄糊涂了。但请重新阅读问题和评论。更新了答案。

SELECT *
FROM books as Book
INNER JOIN books_users as BookUser
    ON BookUser.book_id = Book.id
WHERE
    Book.user_count = 2 AND
    BookUser.user_id IN  (3,18) 

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

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