Question

I have a database of components. Each component is of a specific type. That means there is a many-to-one relationship between a component and a type. When I delete a type, I would like to delete all the components which has a foreign key of that type. But if I’m not mistaken, cascade delete will delete the type when the component is deleted. Is there any way to do what I described?

Answer 1

Here’s what you’d include in your components table.

CREATE TABLE `components` (     `id` int(10) unsigned NOT NULL auto_increment,     `typeId` int(10) unsigned NOT NULL,     `moreInfo` VARCHAR(32),      -- etc     PRIMARY KEY (`id`),     KEY `type` (`typeId`)     CONSTRAINT `myForeignKey` FOREIGN KEY (`typeId`)       REFERENCES `types` (`id`) ON DELETE CASCADE ON UPDATE CASCADE ) 

Just remember that you need to use the InnoDB storage engine: the default MyISAM storage engine doesn’t support foreign keys.