UFN_EVENT_VALIDMAINEVENT

            create function dbo.UFN_EVENT_VALIDMAINEVENT
            (
                @MAINEVENTID uniqueidentifier = null                
            ) 
            returns bit with execute as caller
            as
            begin                
                if @MAINEVENTID is not null begin                     
                    --An event that supports a main event cannot be designated as a main event

                    if (select MAINEVENTID from dbo.EVENT where EVENT.ID = @MAINEVENTID) is not null
                        return 0
                    else
                        return 1
                end 

                return 1
            end