下拉菜单-求php两个下拉列表联动解决办法.

php下拉菜单数据库

选择科室后，对应员工姓名根据选择的科室获取，怎么做到。
两个列表的代码：

```

echo "-请选择-  ";
@include "conn.php"; //链接数据库
$gzh_num_result=mysql_query("select gzh_num , gzh_name from gongzhong where gzh_renum=0 order by gzh_num ;");
while($gzh_num_row=mysql_fetch_array($gzh_num_result))
{

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

<code>    echo "<option value=".$gzh_num.">".$gzh_name."  </option>";        //  echosuboption($gzh_num,@$_GET['gzh_num']);};?>           <td><select name="yg_num">    echo "<option value="0">-请选择-  </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."  ";};?></select></td></code>

<code></code>