function getTables($f = array())
 {
     $where = array();
     if (count($f) > 0) {
         foreach ($f as $t) {
             if ($where != "") {
                 $where .= ' OR ';
             }
             $where[] = '(table_name = "' . $t . '")';
         }
     }
     if (count($where) > 0) {
         $where = ' where ' . implode(" OR ", $where);
     } else {
         $where = '';
     }
     $tb = rex_sql::factory();
     // $tb->debugsql = 1;
     $tb->setQuery('select * from rex_xform_table ' . $where . ' order by prio,name');
     $return = "";
     foreach ($tb->getArray() as $t) {
         $return[$t["table_name"]] = rex_xform_manager_table::factory($t);
         if (!$return[$t["table_name"]]->isValid()) {
             unset($return[$t["table_name"]]);
         }
     }
     return $return;
 }