title: Magento filter product collection by tier price for current customer group
body: <p>How do I filter a product collection by looking at whether a tier price for the current customer group has been set?</p>
  
  <p>I think I need to look at the <code>catalog_product_entity_tier_price</code> table to see if there is an entry for the <code>current customer_group_id</code> for each product in the collection (if there isn't, the product should be excluded / filtered from the collection), but I can't figure out how to make that happen.</p>
  
  <p>Background: Some products are not available to certain customer groups, and we are using tier price to make that determination (i.e. if a tier price exits, include in collection and display, if not, exclude and don't display).</p>
  
  <p>Any help is much appreciated</p>