Du kan bara ha en främmande nyckel som refererar till ett unikt fält. Ändra din network_classes-tabell så att kategorifältet är unikt, som nedan
CREATE TABLE network_classes (
id TINYINT(1) UNSIGNED NOT NULL AUTO_INCREMENT,
category VARCHAR(80) NOT NULL,
PRIMARY KEY(id),
UNIQUE KEY `category_UNIQUE` (`category`),
KEY `key_1` (`id`,`category`)
)
ENGINE=InnoDB;
CREATE TABLE networks (
id TINYINT(3) UNSIGNED NOT NULL AUTO_INCREMENT,
name VARCHAR(100) NOT NULL,
category VARCHAR(80) NOT NULL,
director_id TINYINT(3) UNSIGNED NULL,
director_name VARCHAR(100) NULL,
description VARCHAR(1000) NULL,
last_modified TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
user_id SMALLINT UNSIGNED NULL,
PRIMARY KEY(id),
KEY `networks_fk1` (`category`),
CONSTRAINT `networks_fk1` FOREIGN KEY (`category`) REFERENCES `network_classes` (`category`) ON DELETE NO ACTION,
INDEX networks_index2471(name),
INDEX networks_index2472(director_id, director_name)
)
ENGINE=InnoDB;
Du bör då kunna lägga till den främmande nyckel du vill ha