php选项值链接

I created a dropdown menu and when click on the option on the category in the drop down bar, it can link to my product page, but i failed to linked them, does anyone know what is the problems in my code?

enter code here

$link=mysql_connect("localhost","root","")or die("Can't Connect...");
mysql_select_db("fyp",$link) or die("Can't Connect to Database...");
$query="select * from category ";
$res=mysql_query($query,$link);

while($row=mysql_fetch_assoc($res))
{
    echo "<option value='product.php category=".$roww['$cat_id']."'>".$row['cat_nm'];///here is the problem
    $qq = "select * from subcat where parent_id=".$row['cat_id'];
    $ress = mysql_query($qq,$link) or die("wrong delete subcat query..");
    while($roww = mysql_fetch_assoc($ress))
    {
        echo "<option value='".$roww['subcat_id']."'> ---> ".$roww['subcat_nm'];//here is the problems
    }

}

mysql_close($link);

?>

enter image description here

do it like this, give url you want to edirect to in value and add onchange() to <select>. And you have missed ? which server as query parameter,

 echo "<option value='product.php category=".$roww['$cat_id']."'>".$row['cat_nm'];///here is the problem
                                 ^

it shud be

echo "<option value='product.php?category=".$roww['$cat_id']."'>".$row['cat_nm'];///here is the problem
                                ^

and

<select onchange="this.options[this.selectedIndex].value && (window.location = this.options[this.selectedIndex].value);">
    <option value="">Select...</option>
    <option value="product.php?category=".$roww['$cat_id']."">Product 1</option>
    <option value="product.php?category=".$roww['$cat_id']."">Prosuct 2</option>
</select>

Try this

$link=mysql_connect("localhost","root","")or die("Can't Connect...");
mysql_select_db("fyp",$link) or die("Can't Connect to Database...");
$query="select * from category ";
$res=mysql_query($query,$link);

while($row=mysql_fetch_assoc($res))
{
    echo "<option value='product.php category=".$row['$cat_id']."'>".$row['cat_nm'];///here is the problem
    $qq = "select * from subcat where parent_id=".$row['cat_id'];
    $ress = mysql_query($qq,$link) or die("wrong delete subcat query..");
    while($roww = mysql_fetch_assoc($ress))
    {
        echo "<option value='".$roww['subcat_id']."'> ---> ".$roww['subcat_nm'];//here is the problems
    }

}

mysql_close($link);

?>

Try this and use mysqli instead of mysql, mysql is deprecated(Suggestion)

    $link=mysqli_connect("localhost","root","")or die("Can't Connect...");
    mysqli_select_db($link,"fyp") or die("Can't Connect to Database...");
    $query="select * from category";
    <select onselect='goUrl(this.value)' id="cval" name="cval">
    $res=mysqli_query($link,$query);

    while($row=mysqli_fetch_assoc($res))
    {
       echo "<option value='".$row['cat_id']."'>".$row['maincatname']."</option>";
        $qq = "select * from subcat where parent_id=".$row['cat_id'];
        $ress = mysqli_query($link,$qq) or die("wrong delete subcat query..".mysqli_error($link));
        while($roww = mysql_fetch_assoc($ress))
        {
            echo "----><option value='".$roww['subcat']."'>".$roww['subcatname']."</option>";
        }
    }
    </select>

    mysqli_close($link);

    ?>
    <script>
    function goUrl(catgry)
    {
    window.location.href='product.php?category='+catgry;
    }
    </script>