You need to add an "ALL" option to each drop down list. An easy, but not database-friendly way of doing it is to include "All" as a record in each table so that the user can pick it from the dropdown list. But you probably don't want to add new records in your tables just for the report. So I recommend using a command object and the UNION keyword to build your SQL resultset. For example:

SELECT -999 as Id, "ALL" as Desc 
UNION
SELECT Id, Desc FROM yourtable

Then in your record selection formula you can test for the ALL keyword to select all the record.

{?Parameter}=-999 OR {?Parameter}={table.ProjNo}