Bogus foreign key constraint fail

Question

I get this error message:

ERROR 1217 (23000) at line 40: Cannot delete or update a parent row: a foreign key constraint fails

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Answer 1

Disable foreign key checking

SET FOREIGN_KEY_CHECKS=0

Answer 2

from this blog:

You can temporarily disable foreign key checks:

SET FOREIGN_KEY_CHECKS=0;

Just be sure to restore them once you’re done messing around:

SET FOREIGN_KEY_CHECKS=1;

Answer 3

On demand, now as an answer...

When using MySQL Query Browser or phpMyAdmin, it appears that a new connection is opened for each query (bugs.mysql.com/bug.php?id=8280), making it neccessary to write all the drop statements in one query, eg.

SET FOREIGN_KEY_CHECKS=0; 
DROP TABLE my_first_table_to_drop; 
DROP TABLE my_second_table_to_drop; 
SET FOREIGN_KEY_CHECKS=1; 

Where the SET FOREIGN_KEY_CHECKS=1 serves as an extra security measure...

Answer 4

Cannot delete or update a parent row: a foreign key constraint fails (table1.user_role, CONSTRAINT FK143BF46A8dsfsfds@#5A6BD60 FOREIGN KEY (user_id) REFERENCES user (id))

What i did in two simple steps . first i delete the child row in child table like

mysql> delete from table2 where role_id = 2 && user_id =20;

Query OK, 1 row affected (0.10 sec)

and second step as deleting the parent

delete from table1 where id = 20;

Query OK, 1 row affected (0.12 sec)

By this i solve the Problem which means Delete Child then Delete parent

i Hope You got it. :)

Answer 5

Maybe you received an error when working with this table before. You can rename the table and try to remove it again.

ALTER TABLE `area` RENAME TO `area2`;
DROP TABLE IF EXISTS `area2`;

Answer 6

On Rails, one can do the following using the rails console:

connection = ActiveRecord::Base.connection
connection.execute("SET FOREIGN_KEY_CHECKS=0;")