How make this eav query to make horizontal result

Question

The case:

tables:

product:
product_id|name        |
------------------------
1         |iphone 4    |
2         |gallaxy 2   |
3         |blackbery 6         


        

Answer 1

Let me first say this is a really poor design. Under your current approach, you will need to run multiple subqueries or joins with table aliases to achieve the result you want.

SELECT 
    product_id,
    (
        SELECT product_attribute.value 
        FROM product_attribute, attribute 
        WHERE product_attribute.product_id=product.product_id 
        AND product_attribute.attribute_id=attribute.attribute_id
        AND product_attribute.name = 'width'
    ) AS 'width',
    (
        SELECT product_attribute.value 
        FROM product_attribute, attribute 
        WHERE product_attribute.product_id=product.product_id 
        AND product_attribute.attribute_id=attribute.attribute_id
        AND product_attribute.name = 'height'
    ) AS 'height'
FROM
    product
ORDER BY 
    ...      

Let me suggest:

attribute
   attribute_sid  (eg, string id)

product
   product_id
   name
   ...

product_attribute
   product_id   (foreign key to product table)
   attribute_sid  (foreign key to attribute table)
   value   

This way, you have a definitive list of attributes, and a single attribute value per product.

SELECT attribute_sid, value FROM product_attribute WHERE product_id = 1

... will retrieve all the attributes and values, which can conveniently be placed in a dict, array, or map.