刪除正確的多對多關係

Question

我有一個多對多關係的簡短問題。 這裏是我的表：

+---------+----------------+ 
| 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 | 
+---------+-------------+ 

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

我想要什麼：如果想刪除category，然後在film_category在category_id發生應該刪除，太所有條目。但不是相關的film s！除此之外：這應該工作，同時刪除film反之亦然！ （這正是我的問題就在這裏）

我的問題：我能解決這個問題，只有一個FK-定義或做我必須刪除film_category - 表中的所有條目刪除film或category之前手動？

Answer 1

您的表格應該如下所示。電影表中的刪除應刪除電影類別具有相同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; 

你也應該能夠使用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;