public static function importFromExcel2007($db, $filename)
 {
     $objPHPExcel = PHPExcel_IOFactory::load($filename);
     ExcelImportExport::dropExistingTables($db);
     ExcelImportExport::createTables($db);
     $s1 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'LEHRER');
     $s2 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'ZEITEN');
     $s3 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'SCHUELER');
     $s4 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'SPERRUNGEN');
     $s5 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'RESERVIERUNGEN');
     $s6 = ExcelImportExport::importTableFromExcel($objPHPExcel, 'EINSTELLUNGEN');
     $allInsertStatements = array_merge($s1, $s2, $s3, $s4, $s5, $s6);
     foreach ($allInsertStatements as $statement) {
         ExcelImportExport::$lastExecutedStatement = $statement;
         $db->exec($statement);
     }
     ExcelImportExport::importLehrerKlassen($db);
     ExcelImportExport::writeDefaultSettings($db);
     $temp = '';
     return $temp;
 }