为什么这不起作用？最新查询下拉列表

Question

我有一个下拉列表，我希望它只显示数据库中输入的最新数据。

mysql_select_db($database_final, $final);
$query_LatestPO = "SELECT * FROM tbl_po ORDER BY id_po desc limit 1";
$LatestPO = mysql_query($query_LatestPO, $final) or die(mysql_error());
$row_LatestPO = mysql_fetch_assoc($LatestPO);
$totalRows_LatestPO = mysql_num_rows($LatestPO);

这是我的动态下拉列表的代码

<label>PO Number:</label>
      <select name="select3" id="select3">
        <?php
do {  
?>
<option value="<?php echo $row_LatestPO['id_po']?>">
<?php echo $row_LatestPO['po_no']?></option><?php
} while ($row_LatestPO = mysql_fetch_assoc($LatestPO));
$rows = mysql_num_rows($LatestPO);
if($rows > 0) {
  mysql_data_seek($LatestPO, 0);
  $row_LatestPO = mysql_fetch_assoc($LatestPO);
}
?>
      </select>

为什么这不起作用？它显示下拉列表中表格中的所有数据。