MySQL Removing Some Foreign keys

问题:

I have a table whose primary key is used in several other tables and has several foreign keys to other tables.

CREATE TABLE location (
   locationID INT NOT NULL AUTO_INCREMENT PRIMARY KEY
   ...
) ENGINE = InnoDB;

CREATE TABLE assignment (
   assignmentID INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
   locationID INT NOT NULL,
   FOREIGN KEY locationIDX (locationID) REFERENCES location (locationID)
   ...
) ENGINE = InnoDB;

CREATE TABLE assignmentStuff (
   ...
   assignmentID INT NOT NULL,
   FOREIGN KEY assignmentIDX (assignmentID) REFERENCES assignment (assignmentID)
) ENGINE = InnoDB;

The problem is that when I'm trying to drop one of the foreign key columns (ie locationIDX) it gives me an error.

"ERROR 1025 (HY000): Error on rename"

How can I drop the column in the assignment table above without getting this error?

回答1:

As explained here, seems the foreign key constraint has to be dropped by constraint name and not the index name. The syntax is:

alter table footable drop foreign key fooconstraint

回答2:

The foreign keys are there to ensure data integrity, so you can't drop a column as long as it's part of a foreign key. You need to drop the key first.

I would think the following query would do it:

ALTER TABLE assignmentStuff DROP FOREIGN KEY assignmentIDX;

回答3:

As everyone said above, you can easily delete a FK. However, I just noticed that it can be necessary to drop the KEY itself at some point. If you have any error message to create another index like the last one, I mean with the same name, it would be useful dropping everything related to that index.

ALTER TABLE your_table_with_fk
  drop FOREIGN KEY name_of_your_fk_from_show_create_table_command_result,
  drop KEY the_same_name_as_above

回答4:

Check what's the CONSTRAINT name and the FOREIGN KEY name:

SHOW CREATE TABLE table_name;

Remove both the CONSTRAINT name and the FOREIGN KEY name:

ALTER TABLE table_name
  DROP FOREIGN KEY the_name_after_CONSTRAINT,
  DROP KEY the_name_after_FOREIGN_KEY;

Hope this helps!

回答5:

Here's a way to drop foreign key constraint, it will work. ALTER TABLE location.location_id DROP FOREIGN KEY location_ibfk_1;

回答6:

You usually get this error if your tables use the InnoDB engine. In that case you would have to drop the foreign key, and then do the alter table and drop the column.

But the tricky part is that you can't drop the foreign key using the column name, but instead you would have to find the name used to index it. To find that, issue the following select:

SHOW CREATE TABLE region; This should show you a row ,at left upper corner click the +option ,the click the full text raio button then click the go .there you will get the name of the index, something like this:

CONSTRAINT region_ibfk_1 FOREIGN KEY (country_id) REFERENCES country (id) ON DELETE NO ACTION ON UPDATE NO ACTION Now simply issue an:

alter table region drop foreign key region_ibfk_1;

or

more simply just type:- alter table TableName drop foreign key TableName_ibfk_1;

remember the only thing is to add _ibfk_1 after your tablename to make like this:- TableName_ibfk_1

回答7:

You can not drop the foreign key column because it is being referenced from the table assignmentStuff. So you should first drop the foreign key constraint assignmentStuff.assignmentIDX.

A similar question has already been asked here. Check also here for more info.

回答8:

Try this:

alter table Documents drop
  FK__Documents__Custo__2A4B4B5E

回答9:

step1: show create table vendor_locations;

step2: ALTER TABLE vendor_locations drop foreign key vendor_locations_ibfk_1;

it worked for me.