MySQL moving primary key from varchar to int

Question

I have three tables in MySQL (innodb) (X, Y and Z). X is a table with more than 10 million rows, and has primary key of Y as foreign key. Similarly, Z is table with more than 30 million rows and has primary key of Y as foreign key.

Now the problem is that primary key of Y is VARCHAR (something like a md5 hash or GUID). I want to move this key to INT (AUTO_INCREMENT). What is a way to achieve this in mysql, without writing a script in any other language?

Additionally, primary key of table Z is also a VARCHAR (md5/GUID). I would like to change that to integer as well. (It's not a foreign key in any table).

Answer 1

(This may or may not be any better than Ritobroto's suggestion.)

Assuming X links to Y. (Adapt as needed for all the FKs.)

1. Do something like this for each table.

    ALTER TABLE X DROP FOREIGN KEY ..., -- We'll add it back later ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT, -- Replacement PK DROP PRIMARY KEY, -- Assuming it was `guid` ADD PRIMARY KEY(id), ADD INDEX(X_guid), -- Lost the FK; still (for now) need an index ADD COLUMN Y_id INT UNSIGNED NOT NULL -- future FK to Y ; 

2. Get the new ids linked up (to replace the guids ). For each link:

    UPDATE X JOIN Y ON X.Y_guid = Y.guid SET x.y_id = y.id; 

   (This will take a long time.

3. Re-establish the FKs. For each table:

    ALTER TABLE ... ADD FOREIGN KEY ..., -- to tie `id` instead of `guid` DROP INDEX(X_guid); -- unless you need it for something else 

Practice it on a test machine !!

Answer 2

Step 1
Create tables with same column names but the datatype of primary key of Y should be in INT AUTO INCREMENT ,Same goes for table Z.

Step 2
Use this query:

INSERT INTO table_name (column_names of present table except the primary key column_name) SELECT all the columns except the primary key column FROM Y/Z(which ever table you want from the data to be inserted).

Then you can drop the original table.
It's a painful process for such amount of data,but will do what you have wanted.