UFN_CONSTITUENTID_MAPFROM_REVENUELETTERID

            CREATE function dbo.UFN_CONSTITUENTID_MAPFROM_REVENUELETTERID(@REVENUELETTERID uniqueidentifier) 
            returns uniqueidentifier
            as
            begin
                declare @ID uniqueidentifier;

                select @ID = REVENUE.CONSTITUENTID from dbo.REVENUELETTER
inner join dbo.REVENUE on REVENUE.ID = REVENUELETTER.REVENUEID
where REVENUELETTER.ID = @REVENUELETTERID
;

                RETURN @ID;
            end