$dbh->do("alter session set nls_date_format='YYYY-MM-DD HH24:MI:SS'");
      $dbh->do("alter session set nls_timestamp_format='YYYY-MM-DD HH24:MI:SS.FF'");
      $dbh->do("alter session set nls_timestamp_tz_format='YYYY-MM-DD HH24:MI:SS.FF'");