[mysql] MySQL Removing Some Foreign keys

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?

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;

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

Hey I followed some sequence above, and found some solution.

SHOW CREATE TABLE footable;

You will get FK Constrain Name like

ProjectsInfo_ibfk_1

Now you need to remove this constraints. by alter table commantd

alter table ProjectsInfo drop foreign key ProjectsInfo_ibfk_1;

Then drop the table column,

alter table ProjectsInfo drop column clientId;

first need to get actual constrain name by this query

SHOW CREATE TABLE TABLE_NAME

This query will result constrain name of the foreign key, now below query will drop it.

ALTER TABLE TABLE_NAME DROP FOREIGN KEY COLUMN_NAME_ibfk_1

last number in above constrain name depends how many foreign keys you have in table

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

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.

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

Try this:

alter table Documents drop
  FK__Documents__Custo__2A4B4B5E

step1: show create table vendor_locations;

step2: ALTER TABLE vendor_locations drop foreign key vendor_locations_ibfk_1;

it worked for me.

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!