CODEWITHSUNDEEP
sqlforeign-keysinnodbcascade
Dan
Dan

Reputation: 4140

MySQL InnoDB CASCADE?

I am starting to experiment with using InnoDB in web applications. I've setup some tables with a foreign key, but they are not behaving as expected. Here are my table CREATE statements:

CREATE TABLE sections ( 
    section_id  INT NOT NULL AUTO_INCREMENT, 
    title       VARCHAR(30), 
    created_at  int(10) NOT NULL, 
    updated_at  int(10) NOT NULL,

    PRIMARY KEY(section_id)
) ENGINE=InnoDB; 

CREATE TABLE pages ( 
    page_id       INT NOT NULL AUTO_INCREMENT, 
    section_idfk  INT NOT NULL, 

    PRIMARY KEY(page_id), 
    FOREIGN KEY(section_idfk) REFERENCES sections(section_id) 
    ON DELETE CASCADE 
    ON UPDATE CASCADE
) ENGINE=InnoDB;

The tables create ok and I can populate them with data, however, I was expecting any changes I made to the Sections table to have an effect on the corresponding rows in the Pages table. I tried changing the ID of a section and also deleting a section entirely. In both cases, the Pages table was unaffected.

Can anyone see where I'm going wrong?

Any advice appreciated.
Thanks.

Upvotes: 0

Views: 4360

Answers (1)

itsmatt
itsmatt

Reputation: 31406

I quickly put together two similar tables in the MySQL Query Browser with the following definitions:

DROP TABLE IF EXISTS `test`.`sections`;
CREATE TABLE  `test`.`sections` (
  `section_id` int(10) unsigned NOT NULL auto_increment,
  `title` varchar(30) NOT NULL,
  `created_at` int(10) unsigned NOT NULL,
  `updated_at` int(10) unsigned NOT NULL,
  PRIMARY KEY  (`section_id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

DROP TABLE IF EXISTS `test`.`pages`;
CREATE TABLE  `test`.`pages` (
  `page_id` int(10) unsigned NOT NULL auto_increment,
  `section_idfk` int(10) unsigned NOT NULL,
  PRIMARY KEY  (`page_id`),
  KEY `section_idfk` (`section_idfk`),
  CONSTRAINT `section_idfk` FOREIGN KEY (`section_idfk`) REFERENCES `sections` (`section_id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

Not exactly the same as the ones you posted, but close enough.

I insert into sections a row. I add a row with a matching section_id into the pages table. Then I do a DELETE FROM sections; and it deletes from pages as well.

Works just fine.

edit - I entered your creates and it works fine too.

Upvotes: 2

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