title: Magento - FK_CAT_CTGR_PRD_IDX_PRD_ID_CAT_PRD_ENTT_ENTT_ID foreign key constrait when trying to re-index Category Products
body: <p>The title says it all really - I'm getting an FK constraint failure when trying to re-index Category Products.</p>
  
  <p>Full exception is:</p>
  
  <pre><code>There was a problem with reindexing process.SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails 
  (`krcscouk`.`catalog_category_product_index`, CONSTRAINT `FK_CAT_CTGR_PRD_IDX_PRD_ID_CAT_PRD_ENTT_ENTT_ID` FOREIGN KEY (`product_id`) REFERENCES `catalog_product_entity` (`entity_id`) ON DELETE)
  </code></pre>
  
  <p>I've seen it happen on flat tables before, but never on Category Products, and I'm not sure which tables I'll need to look at to get it playing nicely.</p>