title: woocommerce update sale price
body: <p>I currently have a form where the admin can bulk update sale prices of products within one screen.</p>
  
  <p>When the form is submitted i simply use update_post_meta like this:</p>
  
  <pre><code>update_post_meta($id,'_sale_price', 'new sale price here');
  </code></pre>
  
  <p>This updates the _sale_price meta key. When i go into the admin to check this, the new sale price has been inserted. When i view the product on the front end, the item is not marked as on sale. I have to go back in and re-save the product.</p>
  
  <p>My question is, does woocommerce add some other meta_key to mark the product as on sale? I have had a dig round in the database for all the custom fields inserted, but can only see _sale_price.</p>
  
  <p>Any help would be greatly appreciated</p>