PHP SQL PDO Abfrage über 2 Tabellen, zeigt nur letzt genannte Tabelle an

class bereich {
    public function show_all() {
        $server   = 'mysql:dbname=xxxxxxxxx;host=xxxxxx; port=xxxxx; charset=UTF8';
        $user     = 'xxxxxxxxx';
        $password = 'xxxxxx';
        $options  = array
                (
                  PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
                  //PDO::MYSQL_ATTR_READ_DEFAULT_FILE => '/etc/my.cnf'
                );
        $pdo      = new PDO($server, $user, $password, $options);

        $sql = "Select * FROM wiki_typo3_frontend,wiki_typo3_backend;";
    
        foreach ($pdo->query($sql) as $row) {
            echo "<pre>";
            print_r($row);
            echo "</pre>";
        }
    }
}

(SELECT * FROM Frontend)
UNION
(SELECT * FROMBackend)