I have one primary source and a user id in that source. I now try to blend it with another secondary source with a user if in that source as well to help me blend. Now I have a third source which is a kind of a look up table to help me get some data ( this data has a common field with the second data source). The problem is on one of the views I am creating, I need to have some filters from this third data source as well but Tableau doesnt lets me as it wants me to blend it with my primary source but I dont have any common field to blend it with. I can only only blend it with my secondary source.