我想您需要某种动态查询字符串生成. 尝试将片段从include "config.php";开始替换为:

I guess you need some kind of dynamic query string generation. Try to replace the fragment starts from include "config.php"; to :

include "config.php";
$query = "SELECT kdnr, reklamationsnummer, firma, nachname, vorname, street, hausnummer, postleitzahl, ort, telefon , mail 
          FROM kundentest ";
$search_fields = array('kdnr',
  'reklamationsnummer',
  'firma',
  'nachname',
  'vorname',
  'street',
  'hausnummer',
  'postleitzahl',
  'ort',
  'telefon',
  'mail'
);
$first = true;
$params = array();
foreach ($search_fields as $column) {
    if(isset($_GET[$column])) {
        if ($first) {
            $query.='WHERE ';
            $first = false;
        } else {
            $query.=' AND ';
        }
        $query.= $column.' = ? ';
        $params[]=$_GET[$column];
    }
}

if ($stmt = $mysqli->prepare($query)) {
    $i=0;
    foreach($params as $param) {
        ${'param'.++$i} = $param;
        $stmt->bind_param('s', ${'param'.$i});
    }

     $stmt->execute();

    /* bind result variables */

    $stmt->bind_result($kdnr, $reklamationsnummer, $firma, $nachname, $vorname, $street, $hausnummer, $postleitzahl, $ort, $telefon , $mail);

    while ($stmt->fetch()) { ?>
        <tr>
            <td><?= $kdnr ?></td>
            <td><?= $reklamationsnummer ?></td>
            <td><?= $firma ?></td>
            <td><?= $nachname ?></td>
            <td><?= $vorname ?></td>
            <td><?= $street ?></td>
            <td><?= $hausnummer ?></td>
            <td><?= $postleitzahl ?></td>
            <td><?= $ort ?></td>
            <td><?= $telefon ?></td>
            <td><?= $mail ?></td>
        </tr>
    <?php }
}

如果有任何问题，我们非常欢迎.

you are very welcome if any questions.