留言簿不允许我匿名进入

Question

Problem solved, many thanks for participation

Answer 1

  $StrSQL2 = "SELECT users.benutzername as bn,
  kontakt.betreff, kontakt.nachricht
  FROM users INNER JOIN kontakt
  ON users.userid = kontakt.userid_fk ORDER BY datum DESC";             
  $abfrage = $db->query($StrSQL2);                   
  echo  'Es wurden '.$abfrage->num_rows.' Nachrichten gefunden!<br>';
  while($ausgabe = $abfrage->fetch_object()){
      echo '
      <b>Datum:</b> '.$ausgabe->datum.' <br>
      <b>Betreff:</b> '.$ausgabe->betreff.' <br>
      <b>Nachricht:</b><br> '.$ausgabe->nachricht.' <br>
      <b>Benutzer:</b><br> '.$ausgabe->bn.'<br><hr>'; 
  }

The code that prints the guestbook entries above uses an INNER JOIN. INNER JOIN will only return results that exists on the two table being JOIN-ed which in this case would be users and kontakt. You should use RIGHT JOIN to allow the kontakt retrieved even though it do not have users.

  $StrSQL2 = "SELECT users.benutzername as bn,
  kontakt.betreff, kontakt.nachricht
  FROM users RIGHT JOIN kontakt
  ON users.userid = kontakt.userid_fk ORDER BY datum DESC";

The next problem would be your Benutzer field empty as it originates from the users.benutzername as bn the user table. You could modify the code a little bit to show "Anonymous" if the particular value is null. Something like is_null might worth to try. Your code will be looked like:

  while($ausgabe = $abfrage->fetch_object()){
      echo '
      <b>Datum:</b> '.$ausgabe->datum.' <br>
      <b>Betreff:</b> '.$ausgabe->betreff.' <br>
      <b>Nachricht:</b><br> '.$ausgabe->nachricht.' <br>
      <b>Benutzer:</b><br> '. !is_null($ausgabe->bn) ? $ausgabe->bn : 'Anonymous' .'<br><hr>'; 
  }

The code above uses ternary operator, the ? : pair.

Sorry, i was late to decide to write a proper answer for the question.