Cannot delete or update a parent row: a foreign ke

问题:

When doing:

DELETE FROM `jobs` WHERE `job_id` =1 LIMIT 1 

It errors:

#1451 - Cannot delete or update a parent row: a foreign key constraint fails 
(paymesomething.advertisers, CONSTRAINT advertisers_ibfk_1 FOREIGN KEY 
(advertiser_id) REFERENCES jobs (advertiser_id))

Here are my tables:

CREATE TABLE IF NOT EXISTS `advertisers` (
  `advertiser_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `password` char(32) NOT NULL,
  `email` varchar(128) NOT NULL,
  `address` varchar(255) NOT NULL,
  `phone` varchar(255) NOT NULL,
  `fax` varchar(255) NOT NULL,
  `session_token` char(30) NOT NULL,
  PRIMARY KEY (`advertiser_id`),
  UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;


INSERT INTO `advertisers` (`advertiser_id`, `name`, `password`, `email`, `address`, `phone`, `fax`, `session_token`) VALUES
(1, \'TEST COMPANY\', \'\', \'\', \'\', \'\', \'\', \'\');

CREATE TABLE IF NOT EXISTS `jobs` (
  `job_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `advertiser_id` int(11) unsigned NOT NULL,
  `name` varchar(255) NOT NULL,
  `shortdesc` varchar(255) NOT NULL,
  `longdesc` text NOT NULL,
  `address` varchar(255) NOT NULL,
  `time_added` int(11) NOT NULL,
  `active` tinyint(1) NOT NULL,
  `moderated` tinyint(1) NOT NULL,
  PRIMARY KEY (`job_id`),
  KEY `advertiser_id` (`advertiser_id`,`active`,`moderated`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=2 ;


INSERT INTO `jobs` (`job_id`, `advertiser_id`, `name`, `shortdesc`, `longdesc`, `address`, `active`, `moderated`) VALUES
(1, 1, \'TEST\', \'TESTTEST\', \'TESTTESTES\', \'\', 0, 0);

ALTER TABLE `advertisers`
  ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) REFERENCES `jobs` (`advertiser_id`);

回答1:

As is, you must delete the row out of the advertisers table before you can delete the row in the jobs table that it references. This:

ALTER TABLE `advertisers`
  ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) 
      REFERENCES `jobs` (`advertiser_id`);

...is actually the opposite to what it should be. As it is, it means that you\'d have to have a record in the jobs table before the advertisers. So you need to use:

ALTER TABLE `jobs`
  ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) 
      REFERENCES `advertisers` (`advertiser_id`);

Once you correct the foreign key relationship, your delete statement will work.

回答2:

The simple way would be to disable the foreign key check; make the changes then re-enable foreign key check.

SET FOREIGN_KEY_CHECKS=0; -- to disable them
SET FOREIGN_KEY_CHECKS=1; -- to re-enable them

回答3:

Under your current (possibly flawed) design, you must delete the row out of the advertisers table before you can delete the row in the jobs table that it references.

Alternatively, you could set up your foreign key such that a delete in the parent table causes rows in child tables to be deleted automatically. This is called a cascading delete. It looks something like this:

ALTER TABLE `advertisers`
ADD CONSTRAINT `advertisers_ibfk_1`
FOREIGN KEY (`advertiser_id`) REFERENCES `jobs` (`advertiser_id`)
ON DELETE CASCADE;

Having said that, as others have already pointed out, your foreign key feels like it should go the other way around since the advertisers table really contains the primary key and the jobs table contains the foreign key. I would rewrite it like this:

ALTER TABLE `jobs`
ADD FOREIGN KEY (`advertiser_id`) REFERENCES `advertisers` (`advertiser_id`);

And the cascading delete won\'t be necessary.

回答4:

If you want to drop a table you should execute the following query in a single step

SET FOREIGN_KEY_CHECKS=0; DROP TABLE table_name;

回答5:

I think that your foreign key is backwards. Try:

ALTER TABLE \'jobs\'
ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) REFERENCES `advertisers` (`advertiser_id`)

回答6:

If there are more than one job having the same advertiser_id, then your foreign key should be:

ALTER TABLE `jobs`
ADD CONSTRAINT `advertisers_ibfk_1` 
FOREIGN KEY (`advertiser_id`) 
REFERENCES `advertisers` (`advertiser_id`);

Otherwise (if its the other way round in your case), if you want the rows in advertiser to be automatically deleted if the row in job is deleted add the \'ON DELETE CASCADE\' option to your foreign key

ALTER TABLE `advertisers`
ADD CONSTRAINT `advertisers_ibfk_1` 
FOREIGN KEY (`advertiser_id`) 
REFERENCES `jobs` (`advertiser_id`);
ON DELETE CASCASE

Check out Foreign Key constraints

回答7:

When you create database or create tables

You should add that line at top script create database or table

SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=1;

Now you want to delete records from table? then you write as

SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=1;
DELETE FROM `jobs` WHERE `job_id` =1 LIMIT 1

Good luck!

回答8:

I had this problem in laravel migration too
the order of drop tables in down() method does matter

Schema::dropIfExists(\'groups\');
Schema::dropIfExists(\'contact\');

may not work, but if you change the order, it works.

Schema::dropIfExists(\'contact\');
Schema::dropIfExists(\'groups\');

回答9:

You need to delete it by order There are dependency in the tables

回答10:

How about this alternative I\'ve been using: allow the foreign key to be NULL and then choose ON DELETE SET NULL.

Personally I prefer using both \"ON UPDATE CASCADE\" as well as \"ON DELETE SET NULL\" to avoid unnecessary complications, but on your set up you may want a different approach. Also, NULL\'ing foreign key values may latter lead complications as you won\'t know what exactly happened there. So this change should be in close relation to how your application code works.

Hope this helps.

回答11:

if you need to support client as soon as possible, and do not have access to

FOREIGN_KEY_CHECKS

so that data integrity can be disabled:

1) delete foreign key

ALTER TABLE `advertisers` 
DROP FOREIGN KEY `advertisers_ibfk_1`;

2) activate your deleting operation thruogh sql or api

3) add the foreign key back to schema

ALTER TABLE `advertisers`
  ADD CONSTRAINT `advertisers_ibfk_1` FOREIGN KEY (`advertiser_id`) REFERENCES `jobs` (`advertiser_id`);

however, it is a hot-fix, so it is on your own risk, because the main flaw of such approach is that it is needed afterwards to keep the data integrity manually.

回答12:

You could create a trigger to delete the referenced rows in before deleting the job.

    DELIMITER $$
    CREATE TRIGGER before_jobs_delete 
        BEFORE DELETE ON jobs
        FOR EACH ROW 
    BEGIN
        delete from advertisers where advertiser_id=OLD.advertiser_id;
    END$$
    DELIMITER ;

回答13:

Maybe you should try ON DELETE CASCADE