无法删除表: 外键约束失败

在 MySQL 中，我想删除一个表。
我尝试了很多事情，但是我一直得到的错误是，名为 bericht的表不能被删除。这就是我得到的错误:

# 1217-无法删除或更新父行: 外键约束失败

我怎么把这张桌子弄掉？

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小开

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

小开

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

小开

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.

小开

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.

小开

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.

小开

But fortunately, with the MySQL FOREIGN_KEY_CHECKS variable, you don't have to worry about the order of your DROP TABLE statements at all, and you can write them in any order you like -- even the exact opposite -- like this:

SET FOREIGN_KEY_CHECKS = 0;
drop table if exists customers;
drop table if exists orders;
drop table if exists order_details;
SET FOREIGN_KEY_CHECKS = 1;

For more clarification, check out the link below:

http://alvinalexander.com/blog/post/mysql/drop-mysql-tables-in-any-order-foreign-keys/


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