multiple ordering on categories in Mysql architecture - php

Question

I have a design issue with my Mysql MyISAM tables.
One of my tables contains a list of 'categories', (approx 100 rows)
id |catcode |name
-------------------------------
1 #01 lorem
2 #0101 ipsum
3 #02 dolor
Another table contains 'products'. (approx 28.000 rows)
id |cats |name ...
---------------------------
1 #01#02 lorem ...
2 #0101 ipsum ...
3 #02#0101 dolor ...
in my products table, I define the list of categories where they belong to.
that's working perfectly, but now:
I'd like to customize the ordering they appear depending on the category selected.
At the moment, I have a column with the id of the categorie in my product table, but this seams very dirty (ordering_1, ordering_2, ordering_3, ...)
Especially because each product appears in only 2 or 3 different categories, so most of the columns are just empty:
id |cats |name |ordering_1 |ordering_2 |ordering_3 ...
-----------------------------------------------------------------------
1 #01#02 lorem 17 12
2 #0101 ipsum 13
3 #02#0101 dolor 21 8
I'd like to use a third table to determine the ordering, but how?
The basic idea is to have a table with the categories and an 'ordering' list, but one of these lists contains all the products! (the main category) I suppose it would be veeery slow to do a request with 28.000 id in it...
How to handle this?

Answer 1

You should use foreign keys and a join table to link products with categories, instead of your catcode construct.
Create the table structure somewhat like the following (example is for MySQL):
CREATE TABLE product (
id INT NOT NULL,
name VARCHAR(255),
PRIMARY KEY (id)
) ENGINE=InnoDB;
CREATE TABLE category (
id INT NOT NULL,
name VARCHAR(255),
PRIMARY KEY (id)
) ENGINE=InnoDB;
CREATE TABLE product_category (
product_id INT NOT NULL,
category_id INT NOT NULL,
ordering INT NOT NULL,
PRIMARY KEY (product_id, category_id),
FOREIGN KEY (product_id) REFERENCES product (id),
FOREIGN KEY (category_id) REFERENCES category (id)
) ENGINE=InnoDB;
Then to get all products in a particular category sorted as defined for this category, query them like this:
SELECT * FROM product p LEFT JOIN product_category pc ON p.id = pc.product_id
WHERE pc.category_id = 1
ORDER BY pc.ordering ASC;
1 is the category id in this. You could also query by category name for example:
SELECT * FROM product p
LEFT JOIN product_category pc ON p.id = pc.product_id
LEFT JOIN category c ON pc.category_id = c.id
WHERE c.name = "foo"
ORDER BY pc.ordering ASC;