CODEWITHSUNDEEP
phpmysqlmigration
rcs20
rcs20

Reputation: 605

mysql separating tables

i made a mistake and i have to split 1 table into 2. i have a product table and i need category table. when i started i only had 1 category per product but not (with new business requirement) i need the ability to put a product in multiple category.

i have a product tables that has a category in it.

here's the table:

product (id, name, category, price etc...)

now, how can i efficiently migrate this without make my site offline?

i have lamp on centos

Upvotes: 18

Views: 257

Answers (4)

dar7yl
dar7yl

Reputation: 3747

You would start by normalizing your product table - creating 2 new tables:

CREATE TABLE categories
(
  cat_id int AUTO_INCREMENT NOT NULL PRIMARY KEY,
  cat_label varchar(40)
);

CREATE TABLE product_by_category
(
  pbc_prod_id int REFERENCES products(id),
  pbc_cat_id int REFERENCES categories(cat_id),
  #indexes for quicker lookup...
  INDEX pbc(pbc_prod_id,pbc_cat_id),
  INDEX cbp(pbc_cat_id, pbc_prod_id)
);



  INSERT INTO categories(cat_label) SELECT DISTINCT category FROM product;
   INSERT INTO product_by_category(pbc_prod_id, pbc_cat_id)
      SELECT id, (SELECT cat_id FROM categories WHERE categories.cat_label = product.category)
      FROM products;

    ALTER TABLE products DROP COLUMNN category;  #do this after you are satisfied with contents of new tables.

Then you would have to create joins for getting products by category.

Upvotes: 0

Book Of Zeus
Book Of Zeus

Reputation: 49885

First make sure your categories are unique. Make sure you don't have something like: 

productx and produtx

Otherwise, when you will inserts bad categories.

You will have to do it in step:

1) Creating the table category

CREATE TABLE `category` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `name` varchar(40) NOT NULL DEFAULT 'General',
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

Create the intersection table since a product can be in multiple category and a category can have multiple product.

CREATE TABLE `product_category` (
  `product_id` int(10) unsigned NOT NULL,
  `category_id` int(10) unsigned NOT NULL,
 PRIMARY KEY product_category (`product_id`,`category_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

2) inserts the categories into the table.

INSERT IGNORE INTO category SELECT DISTINCT category from product;

This will insert non duplicate categories into the category table with a unique id.

Now, you have to inserts these records in the

INSERT IGNORE INTO `product_category` SELECT `product`.`id` AS `product_id`, `category`.`id` AS `category_id` FROM `category` LEFT JOIN `product` ON (`category`.`name` = `product`.`category`);

3) Now you have to modify your code in order to use the right query: Example:

SELECT 
 /* your fields */
FROM
product
INNER JOIN product_category ON (product.id = product_category.product_id)
INNER JOIN category ON (category.id = product_category.category_id)
WHERE ...

4) Now, when you feel comfortable with your code changes, you can drop the unused column:

ALTER TABLE product DROP COLUMN category;

Upvotes: 24

Dennis
Dennis

Reputation: 4017

INSERT INTO new_table_name ("product", "category")
SELECT id, category
FROM product;

Then add a foriegn key constraint on id in new_table_name which references the original product table. After this you can alter table product drop column column_name.

Upvotes: 0

favoretti
favoretti

Reputation: 30167

Create a table category:

CREATE TABLE category(id int primary key not null auto_increment, category varchar(40))

Then select unique categories from product table:

INSERT INTO category (category) SELECT DISTINCT category FROM product;

Then create a table for relations: 

CREATE TABLE product_to_category (product_id int, category_id int);

If you want, you can use foreign keys and constraints.

Then you can migrate your existing relations:

INSERT INTO product_to_category SELECT product.id, category.id FROM product JOIN category on category.category=product.category;

After that, adjust your code to use the new structure and drop the category column from product table:

ALTER TABLE product DROP COLUMN category;

Hope this helps.

Upvotes: 3

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