.
...
To change the main query so that it will return all the records if no parameter is chosen, change the WHERE clause of the query from 'WHERE SalesPersonID=@SalesPersonID' to 'WHERE (SalesPersonID=@SalesPersonID OR @SalesPersonID=0)' (remember, zero was our default value).
Samples
Download an .rdl file created with Microsoft Query and OfficeWriter.Download an .rdl file created with Visual Studio and OfficeWriter.
...