I'm not sure if it's exactly what you mean, but since there would be no way to define WHEN "all data items are dragged on to the reporting area" there is the "Run Report" link to the left in Query Studio, and from within that menu, there's a "Preview with No Data" option which would let you add in all of the data items that you need before any query is sent to the database. When you're finished developing the query, then you would navigate to the "Run Report" menu again and click "run with all data"