循环中间加入字符的有关问题

while ($down=mysql_fetch_array($downser)){     
  $kb_data_glay .= $down[goods_sn].'$'.$down[goods_name]."','";
}
$kb_data_glay = substr($kb_data_glay, 0, -1);

while ($down=mysql_fetch_array($downser)){     
  $kb_data_glay[] = $down[goods_sn].'$'.$down[goods_name];
}
$kb_data_glay = join(',', $kb_data_glay);