下拉菜單-求php兩個下拉列表聯動解決辦法.

求php兩個下拉列表聯動解決辦法.

選擇科室後，對應員工姓名根據選擇的科室獲取，怎麼做到。
兩個列表的代碼：

```

echo "-請選擇-  ";
<?php
@include "conn.php"; //鏈接數據庫
$gzh_num_result=mysql_query("select gzh_num , gzh_name from gongzhong where gzh_renum=0 order by gzh_num ;");
while($gzh_num_row=mysql_fetch_array($gzh_num_result))
{

list($gzh_num,$gzh_name)=$gzh_num_row;

    echo "<option value=".$gzh_num.">".$gzh_name."&nbsp;&nbsp;</option>";
        //  echosuboption($gzh_num,@$_GET['gzh_num']);

};
?>
</select>
    </td>   
    <td><select name="yg_num" >
    echo "<option value=0>-請選擇-&nbsp;&nbsp;</option>";
      <?php

$yg_num_result=mysql_query("select yg_num , yg_name from yuangong where gzh_renum=01 order by yg_num ;");
while($yg_num_row=mysql_fetch_array($yg_num_result))
{   
    list($yg_num,$yg_name)=$yg_num_row;

    echo "<option value=".$yg_num.">".$yg_name."&nbsp;&nbsp;</option>";

};
?>
</select></td>

最佳回答：

gzh__rum處應當寫什麼代碼可以實現？