MySQL Removing Some Foreign keys

Question

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?

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

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;

Answer 5

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!

Answer 6

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.