title: Magento - Difference between url_path and url_key
body: <p>Pretty much everything is in the title of my question. </p>
  
  <p>What is the difference between the columns <code>url_path</code> and <code>url_key</code> in the flat products tables - like catalog_product_flat_(store_id) - of Magento ? </p>
  
  <p>Thanks !</p>