If you need find a products what not applied to website you can execute this query and it return a list of all product ids whta not applied to any website. Can also improve this query for retrieve any need fileds besides entity_id like a sku etc, or can set specific website id for check it.


  SELECT entity_id 
  FROM catalog_product_entity AS cpe 
  LEFT JOIN catalog_product_website AS cpw 
  ON cpw.product_id = cpe.entity_id 
  WHERE cpw.product_id IS NULL

Read about the SQL JOIN for more info.