MySQL: delete a row ignoring foreign key constraint
so I am working on a few tables and there are some data inconsistency between them... One or two tables have a foreign key constraint on a particular table (call it table X), but that table has multiple rows with the foreign key column.
What I want to do is to remove the duplicated rows in table X, but the foreign key constraint is preventing me from doing this. Is there a way to force delete the rows while ignoring the foreign key constraint since I know what I'm doing?
Solution 1:
SET foreign_key_checks = 0;
That will prevent MySQL from checking foreign keys. Make sure to set it back to 1 when you are done though.
Also, you could always drop the foreign key and then add it later if you wanted to only affect a singular key
ALTER TABLE tableName DROP FOREIGN KEY fk;
Solution 2:
Simply execute as follows:
-
Disable foreign key check
SET foreign_key_checks = 0;
-
Delete your records
DELETE FROM table_name WHERE {conditions};
-
Enable foreign key check
SET foreign_key_checks = 1;
Credit: https://www.knowledgewalls.com/johnpeter/books/mysql/how-to-ignore-constraints-while-insertupdate-or-delete-records-in-mysql
Solution 3:
As some people already pointed out, ignoring a restricting foreign key leaves you with database inconsistencies. Preventing DELETE
s is something you want in such cases.
You should better delete depending rows prior to the main query:
DELETE FROM cities WHERE country_id=3;
-- Afterwards you delete rows from the parent table without error:
DELETE FROM countries WHERE country_id=3;
Or, even better, change the foreign key once, so it does the deletion automatically (cascading):
ALTER TABLE cities DROP FOREIGN KEY `fk.cities.country_id`;
ALTER TABLE cities ADD CONSTRAINT `fk.cities.country_id` FOREIGN KEY (country_id)
REFERENCES countries (id) ON UPDATE CASCADE ON DELETE CASCADE;
-- From now on, just delete from the parent table:
DELETE FROM countries WHERE country_id=3;