你试一下
<select name="class_id" onChange="javascript:{location='<? echo $PHP_SELF ?>?class_id='+this.value;}" class="blue">
<select name="class_id" onChange="javascript:{location='<? echo $PHP_SELF ?>?class_id='+this.value;}" class="blue">
连接数据库的略
<?php
$sql="select * from mallclass";
$result=mysql_query($sql);
$myrow=mysql_fetch_array($result);
echo("<option value=\"请选择手机品牌\">---请选择手机品牌---</option>");
do
{
$class_id=$myrow["class_id"];
$class_name=$myrow["class_name"];
echo ("<option value=$class_name>$class_name</option>");
}while($myrow=mysql_fetch_array($result));?>