Get sold items, ordered by purchases, in the last week - mysql

Question

I have 2 Tables.
The first table stores the products.
id I Product Name
1 I Apple
2 I Bread
3 I Butter
... Many more
The second table stores the overall purchases with a date
product_id I purchasedoverall I date
1 I 2 I 1.2.14
1 I 10 I 3.2.14
3 I 3 I 4.2.14
... Many more
Attention: In the example, at 1.2.14 2 apples where sold, at 3.2.14 8 more apples, so there are 10 stored in purchasedoverall.
What I want from the Database is:
Give me the products purchased in the last week, ordered by how many items where bought IN THE LAST WEEK.
Until now, I do it this (bad) way:
I get all products
SELECT * FROM products
Store them in an array
I iterate over the array to get the purchased count in the last week
SELECT MAX(c.purchasedoverall)-MIN(c.purchasedoverall) as purchased
FROM products as a, puchased as c
WHERE c.product_id = {product-id from the array}
AND c.date >= NOW() - INTERVAL 1 WEEK
ORDER BY c.date
I combine the arrays an sort them
My question: Can I do this with one MySQL-Query?

Answer 1

Assuming pr.name is unique:
SELECT pr.name,
COALESCE(MAX(pu.purchasedoverall)-MIN(pu.purchasedoverall),0) purchased
FROM products pr
LEFT JOIN purchased pu
ON pu.product_id = pr.id
AND pu.date > CURDATE() - INTERVAL 1 WEEK
GROUP BY pr.name
ORDER BY purchased DESC, pr.name
But as pointed out in the comments you should really be storing data at the resolution that you need it, not performing complex queries to enhance the resolution..
Whatever the difficulties of obtaining the data structure and the code associated, it is almost certainly much easier to refactor this than build a system atop a flawed design.

Answer 2

SELECT a.id, a.product_name, MAX(c.purchasedoverall)-MIN(c.purchasedoverall) as total_purchased
FROM products a
left join puchased c
ON c.product_id=a.id
AND c.date >= NOW() - INTERVAL 1 WEEK
group by a.id
ORDER BY total_purchased;