How do I use on delete cascade in mysql?
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21-08-2019 - |
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?
Solution
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.
OTHER TIPS
You have to define your Foreign Key constraints as ON DELETE CASCADE.
Note: You need to use InnoDB storage engine, he default MyISAM storage engine not support foreign keys relation.
CREATE TABLE `table2` (
`id` int(11) NOT NULL auto_increment,
`name` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `ids` (`ids`)
CONSTRAINT `foreign` FOREIGN KEY (`ids`)
REFERENCES `table2` (`ids`) ON DELETE CASCADE ON UPDATE CASCADE
)
use this sql
DELETE T1, T2 FROM T1 INNER JOIN T2 ON T1.key = T2.key WHERE condition