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

There are several ways to implement this. Something like this should work joining back on the table multiple times for each attribute value:

SELECT p.product_id,
    a.value height,
    a2.value width
FROM Product p
    JOIN Product_Attribute pa ON p.product_id = pa.product_id 
    JOIN Attribute a ON pa.attribute_id = a.attribute_id AND a.name = 'height'
    JOIN Product_Attribute pa2 ON p.product_id = pa2.product_id 
    JOIN Attribute a2 ON pa2.attribute_id = a2.attribute_id AND a2.name = 'width'

And here is the Fiddle.

Here is an alternative approach using MAX and GROUP BY that I personally prefer:

SELECT p.product_id,
    MAX(Case WHEN a.name = 'height' THEN a.value END) height,
    MAX(Case WHEN a.name = 'width' THEN a.value END) width
FROM Product p
    JOIN Product_Attribute pa ON p.product_id = pa.product_id 
    JOIN Attribute a ON pa.attribute_id = a.attribute_id 
GROUP BY p.product_id

Good luck.