I'd recommend, to change your database schema. Why?
Can a book exist without having a user? If yes, you shouldn't have a foreign key from books referencing users. Can a user exist without having a book? If yes, you shouldn't have a foreign key from users referencing books.
Can a user have multiple books? And a book multiple users? If yes, you have a m:n relationship. This means you need a bridge table.
In your tables you don't need foreign keys:
CREATE TABLE `Users` (
`user_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`first_name` varchar(50) NOT NULL DEFAULT '',
`last_name` varchar(50) NOT NULL DEFAULT '',
`login` varchar(50) NOT NULL DEFAULT '',
`password` varchar(50) NOT NULL DEFAULT '',
PRIMARY KEY (`user_id`)
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8;
CREATE TABLE `Books` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(50) NOT NULL DEFAULT '',
`author` varchar(50) NOT NULL DEFAULT '',
`year` int(4) NOT NULL,
`available` int(3) NOT NULL DEFAULT '0',
`availabledate` date NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
And a bridge table would look like this:
CREATE TABLE books_users (
book_id int(11) unsigned NOT NULL,
user_id int(11) unsigned NOT NULL,
PRIMARY KEY (book_id, user_id),
KEY idx_user_id (user_id),
FOREIGN KEY fk_books (book_id) REFERENCES Books(id),
FOREIGN KEY fk_users (user_id) REFERENCES Users(user_id)
) ENGINE=InnoDB;
This solves both problems and is common practice.
To query both users and books in one query, you join them like this:
SELECT
whatever
FROM
Books b
INNER JOIN books_users bu ON b.id = bu.book_id
INNER JOIN users u ON bu.user_id = u.user_id
WHERE user_id = 1 /*for example*/
;
If you want to insert something in the tables, just do the insert and get the id which was generated for the row with SELECT LAST_INSERT_ID();
, then insert this id in the books_users
bridge table.
Updates don't affect anything, you can simply perform them on users
or books
. If you really really have to update the auto_increment column (which usually isn't needed and not recommended) you can add ON UPDATE CASCADE
after the foreign keys in the books_users
table.