title: Get the largest discounts using sql query
body: <p>I have a lot of products in my table. Some of products has a discount, so in <code>price_old</code> field is given old price of the product, and the <code>price</code> field has a new discounted price. </p>
  
  <p>Is it posible to get all products, arranged by the biggest difference(discount) between fields <code>price_old</code> and <code>price</code>?</p>