删除正确的多对多关系

Question

我有一个多对多关系的简短问题。 这里是我的表：

+---------+----------------+ 
| film_id | title   | 
+---------+----------------+ 
|  1 | Apocalypse Now | 
+---------+----------------+ 


+-------------+----------------------+ 
| category_id | name     | 
+-------------+----------------------+ 
|   1 | cool category  | 
+-------------+----------------------+ 
|   2 | not so cool category | 
+-------------+----------------------+ 

+---------+-------------+ 
| film_id | category_id | 
+---------+-------------+ 
|  1 |   1 | 
+---------+-------------+ 
|  1 |   2 | 
+---------+-------------+ 

正如你可以看到有从film FKS - 和category -table在film_category - 表。

我想要什么：如果想删除category，然后在film_category在category_id发生应该删除，太所有条目。但不是相关的film s！除此之外：这应该工作，同时删除film反之亦然！ （这正是我的问题就在这里）

我的问题：我能解决这个问题，只有一个FK-定义或做我必须删除film_category - 表中的所有条目删除film或category之前手动？

Answer 1

您的表格应该如下所示。电影表中的删除应删除电影类别具有相同ID的行，反之亦然。

CREATE TABLE `film` (
    `film_id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
    `title` varchar(255) NOT NULL DEFAULT '', 
    PRIMARY KEY (`film_id`) 
) ENGINE=InnoDB; 

CREATE TABLE `category` (
    `category_id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
    `name` varchar(255) NOT NULL DEFAULT '', 
    PRIMARY KEY (`category_id`) 
) ENGINE=InnoDB; 

CREATE TABLE `film_category` (
`film_category_id` int(10) unsigned NOT NULL AUTO_INCREMENT, 
`film_id` int(10) unsigned NOT NULL DEFAULT '0', 
`category_id` int(10) unsigned NOT NULL DEFAULT '0', 
PRIMARY KEY (`film_category_id`), 
KEY `film_id` (`film_id`), 
KEY `category_id` (`category_id`), 
CONSTRAINT `film_category_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `category` (`category_id`) ON DELETE CASCADE, 
CONSTRAINT `film_category_ibfk_1` FOREIGN KEY (`film_id`) REFERENCES `film` (`film_id`) ON DELETE CASCADE 
) ENGINE=InnoDB; 

你也应该能够使用film_category如下：

CREATE TABLE `film_category` (
    `film_id` int(10) unsigned NOT NULL DEFAULT '0', 
    `category_id` int(10) unsigned NOT NULL DEFAULT '0', 
    PRIMARY KEY (`film_id`,`category_id`), 
    CONSTRAINT `film_category_ibfk_1` FOREIGN KEY (`film_id`) REFERENCES `film` (`film_id`) ON DELETE CASCADE, 
    CONSTRAINT `film_category_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `category` (`category_id`) ON DELETE CASCADE 
) ENGINE=InnoDB;