Mysql error 1452 - Cannot add or update a child row: a foreign key constraint fails

user_144259 0
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I'm having a bit of a strange problem. I'm trying to add a foreign key to one table that references another, but it is failing for some reason. With my limited knowledge of MySQL, the only thing that could possibly be suspect is that there is a foreign key on a different table referencing the one I am trying to reference.

I've done a SHOW CREATE TABLE query on both tables, sourcecodes_tags is the table with the foreign key, sourcecodes is the referenced table.

CREATE TABLE `sourcecodes` (
 `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
 `user_id` int(11) unsigned NOT NULL,
 `language_id` int(11) unsigned NOT NULL,
 `category_id` int(11) unsigned NOT NULL,
 `title` varchar(40) CHARACTER SET utf8 NOT NULL,
 `description` text CHARACTER SET utf8 NOT NULL,
 `views` int(11) unsigned NOT NULL,
 `downloads` int(11) unsigned NOT NULL,
 `time_posted` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
 PRIMARY KEY (`id`),
 KEY `user_id` (`user_id`),
 KEY `language_id` (`language_id`),
 KEY `category_id` (`category_id`),
 CONSTRAINT `sourcecodes_ibfk_3` FOREIGN KEY (`language_id`) REFERENCES `languages` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `sourcecodes_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `sourcecodes_ibfk_2` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1

CREATE TABLE `sourcecodes_tags` (
 `sourcecode_id` int(11) unsigned NOT NULL,
 `tag_id` int(11) unsigned NOT NULL,
 KEY `sourcecode_id` (`sourcecode_id`),
 KEY `tag_id` (`tag_id`),
 CONSTRAINT `sourcecodes_tags_ibfk_1` FOREIGN KEY (`tag_id`) REFERENCES `tags` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=latin1

This is the code that generates the error:

ALTER TABLE sourcecodes_tags ADD FOREIGN KEY (sourcecode_id) REFERENCES sourcecodes (id) ON DELETE CASCADE ON UPDATE CASCADE
mysql-error-1452 foreign-keys mysql
21 Answers

Quite likely your sourcecodes_tags table contains sourcecode_id values that no longer exists in your sourcecodes table. You have to get rid of those first.

Here's a query that can find those IDs:

SELECT DISTINCT sourcecode_id FROM 
   sourcecodes_tags tags LEFT JOIN sourcecodes sc ON tags.sourcecode_id=sc.id 
WHERE sc.id IS NULL;
user_1267690

you can try this exapmple

 START TRANSACTION;
 SET foreign_key_checks = 0;
 ALTER TABLE `job_definers` ADD CONSTRAINT `job_cities_foreign` FOREIGN KEY 
 (`job_cities`) REFERENCES `drop_down_lists`(`id`) ON DELETE CASCADE ON UPDATE CASCADE;
 SET foreign_key_checks = 1;
 COMMIT;

Note : if you are using phpmyadmin just uncheck Enable foreign key checks

as example enter image description here

hope this soloution fix your problem :)

user_20773500

In my case, I created a new table with the same structure, created the relationships with the other tables, then extracted the data in CSV from the old table that has the problem, then imported the CSV to the new table and disabled foreign key checking and disabled import interruption, all my data are inserted to the new table that has no problem successfully, then deleted the old table.

It worked for me.

user_14144230
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