Dave Airel  Can you make a last effort to try the following script?

do as server
  let x := select Contacts;
  let y := select Events;
  let z := select RSVP;
  for i in select StagingImport do
      let c := if contains(x.Email, i.Email) then
                   first(x[Email = i.Email])
               else
                   create Contacts.(
                       Email := i.Email;
                       Lastname := i.'Last name';
                       Firstname := i.'First name';
                       'Mobile Phone' := i.'Mobile number';
                       Zip := i.Zip)
               end;
      let e := if contains(y.'Event ID', i.'Event ID') then
                   first(y['Event ID' = i.'Event ID'])
               else
                   let w := create Events.(
                       'Event ID' := i.'Event ID';
                       'Event Name' := i.'Event name';
                       'Event Type' := i.'Event type';
                       'Date / Time' := i.'Event Start Date');
                   y := array(y,w);
                    w
               end;
       if count(z[Attended = i.Attended and Contacts = number(c.Id) and Events = number(e.Id)]) = 0 then
                   create RSVP.(
                       Contacts := number(c.Id);
                       Events := number(e.Id);
                       Attended := i.Attended);
       end;
  end;
  delete select StagingImport;
end

On a side note, if you are on a Mac you can use the MacOS app to download copies of your DB regardless of the level of your subscription.

Dave AirelFredRoSoft_Steven

I think we're getting there. The issue came up because the 'select' statement returns 'nid', but the 'create' statement returns 'rid'. Here's a script you can try out.

do as server
    let x := (select Contacts);
    let y := (select Events);
    let z := (select RSVP);
    for i in select StagingImport do
        let c := if contains(x.Email, i.Email) then
                first(x[Email = i.Email])
            else
                (create Contacts).(
                    Email := i.Email;
                    Lastname := i.'Last name';
                    Firstname := i.'First name';
                    'Mobile Phone' := i.'Mobile number';
                    Zip := i.Zip
                )
            end;
        let e := if contains(y.'Event ID', i.'Event ID') then
                first(y['Event ID' = i.'Event ID'])
            else
                let w := (create Events);
                w.(
                    'Event ID' := i.'Event ID';
                    'Event Name' := i.'Event name';
                    'Event Type' := i.'Event type';
                    'Date / Time' := i.'Event Start Date'
                );
                y := array(y, [w.Id]);
                w.Id
            end;
        if count(z[Attended = i.Attended and Contacts = number(c.Id) and Events = number(e.Id)]) = 0 then
            (create RSVP).(
                Contacts := number(c.Id);
                Events := number(e.Id);
                Attended := i.Attended
            )
        end
    end;
    delete (select StagingImport)
end

Dave Airel  

We should use the same logic in the Contacts table. If a new contact attends multiple events in the .csv file, only one new record should be created in the Contacts Table. I updated the script and made the names a bit more descriptive.

do as server
    let allContacts := (select Contacts);
    let allEvents := (select Events);
    let allRSVP := (select RSVP);
    for i in select StagingImport do
        let contact := if contains(allContacts.Email, i.Email) then
                first(allContacts[Email = i.Email])
            else
                let newContact := (create Contacts);
                newContact.(
                    Email := i.Email;
                    Lastname := i.'Last name';
                    Firstname := i.'First name';
                    'Mobile Phone' := i.'Mobile number';
                    Zip := i.Zip
                );
                allContacts := array(allContacts, [newContact.Id]);
                newContact.Id
            end;
        let event := if contains(allEvents.'Event ID', i.'Event ID') then
                first(allEvents['Event ID' = i.'Event ID'])
            else
                let newEvent := (create Events);
                newEvent.(
                    'Event ID' := i.'Event ID';
                    'Event Name' := i.'Event name';
                    'Event Type' := i.'Event type';
                    'Date / Time' := i.'Event Start Date'
                );
                allEvents := array(allEvents, [newEvent.Id]);
                newEvent.Id
            end;
        if count(allRSVP[Attended = i.Attended and Contacts = number(contact.Id) and Events = number(event.Id)]) = 0 then
            (create RSVP).(
                Contacts := number(contact.Id);
                Events := number(event.Id);
                Attended := i.Attended
            )
        end
    end;
    delete (select StagingImport)
end

I've attached my demo database where I did all the testing. I'm eager to hear the results from your database. Are you having any other problems?

Dave Airel  We made it!

The issue in your database came up because the 'Event ID' field in the StagingImport table was set to number data type. So, I changed it to a text field type.

Everything seems to be working as expected now. Are you happy with the final result?

Today, I learned how to add a newly created record to an array of selected records using code. I have to thank  Jacques TUR  for his helpful contribution.

I've attached the updated version of your database.

Best wishes