Can't drop table: A foreign key constraint fails

Question

In MySQL I want to drop a table.
I tried a lot things but I keep getting the error that the table named bericht can't be dropped. This is the error I'm getting:

#1217 - Cannot delete or update a parent row: a foreign key constraint fails

How do I drop this table?

Answer 1

This should do the trick:

SET FOREIGN_KEY_CHECKS=0; DROP TABLE bericht; SET FOREIGN_KEY_CHECKS=1;

As others point out, this is almost never what you want, even though it's whats asked in the question. A more safe solution is to delete the tables depending on bericht before deleting bericht. See CloudyMarble answer on how to do that. I use bash and the method in my post to drop all tables in a database when I don't want to or can't delete and recreate the database itself.

The #1217 error happens when other tables has foreign key constraints to the table you are trying to delete and you are using the InnoDB database engine. This solution temporarily disables checking the restraints and then re-enables them. Read the documentation for more. Be sure to delete foreign key restraints and fields in tables depending on bericht, otherwise you might leave your database in a broken state.

Answer 2

Try this:

SELECT * 
FROM information_schema.KEY_COLUMN_USAGE 
WHERE REFERENCED_TABLE_NAME = 'YourTable';

This should deliver you which Tables have references to the table you want to drop, once you drop these references, or the datasets which reference datasets in this table you will be able to drop the table

Answer 3

Use show create table tbl_name to view the foreign keys

You can use this syntax to drop a foreign key:

ALTER TABLE tbl_name DROP FOREIGN KEY fk_symbol

There's also more information here (see Frank Vanderhallen post): http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html

Answer 4

This probably has the same table to other schema the reason why you're getting that error.

You need to drop first the child row then the parent row.

Answer 5

I realize this is stale for a while and an answer had been selected, but how about the alternative to allow the foreign key to be NULL and then choose ON DELETE SET NULL.

Basically, your table should be changed like so:

ALTER TABLE 'bericht' DROP FOREIGN KEY 'your_foreign_key';

ALTER TABLE 'bericht' ADD CONSTRAINT 'your_foreign_key' FOREIGN KEY ('column_foreign_key') REFERENCES 'other_table' ('column_parent_key') ON UPDATE CASCADE ON DELETE SET NULL;

Personally I would recommend using both "ON UPDATE CASCADE" as well as "ON DELETE SET NULL" to avoid unnecessary complications, however your set up may dictate a different approach.

Hope this helps.