How to make cascading drop-down lists using mysql and php

Question

I have to make a form with multiple drop-down menus that modify one another. The menus/database tables are:

Categories, Styles, Types, and Mechanisms

I have

Answer 1

option must be array.

$options[]="<OPTGROUP LABEL=\"$category_name\"> <br />";
<SELECT NAME="category_id">
   <?php foreach ($options as $value) 
           echo $value?>
</SELECT>

Answer 2

Finally just had to figure it out on my own, but thanks for those who tried to help.

I will post my middle table from my Class/Category/Style/Type cascading tables. First make a function such as the below:

 <?php //Category Selection
    function Category_Selection($link) {
        global $connection;
        $options="";
        if(isset($_GET["class_id"])) {
            $query="SELECT categories.category_id, categories.Category_Name ";
            $query.="FROM categories ";
            $query.="ORDER BY categories.Category_Name ASC";
            $result=mysql_query($query, $connection);
            $class_id=$_GET['class_id'];

            if(!$result){
                die("Database query failed: " . mysql_error());
            }
            while ($row=mysql_fetch_array($result)) {
                $name=$row["Category_Name"];
                $id=$row["category_id"];
                $link2=$link."&category_id={$id}";
                $options.="<OPTION VALUE=\"$link2\" ";
                if(isset($_GET["category_id"])) {
                    $category_id = $_GET['category_id'];
                    if($id==$category_id) {
                        $options.=" selected=\"selected\" ";
                    }
                }
                $options.=" >".$name.'</OPTION>';
            }
        } else {
            $options.="<OPTION selected=\"selected\" VALUE=0>First Select Class</OPTION>";
        }
        return($options);
    }
?>

Then place on your main page:

<?php session_start() ?>
    //Category
    if(isset($_GET['category_id'])) {
        $category_id=$_GET['category_id'];
        setcookie('category_id',$category_id);
        $link.="&category_id={$category_id}";
    }elseif(isset($_COOKIE['category_id'])) {
        $_GET['category_id']=$_COOKIE['category_id'];
        $category_id=$_COOKIE['category_id'];
        $link.="&category_id={$category_id}";
    }

Now make your selection drop-down:

<?php //Category Selection
                $options=Category_Selection($link);
            ?>
            <center>
            <SELECT NAME="category_id" ONCHANGE="location = this.options[this.selectedIndex].value;">
                <OPTION VALUE=0></OPTION>
                <?php echo $options ?>
            </SELECT>
            </center>

Repeat above for each required drop-down.

Good luck...and, of course use MYSQLi to protect your site rather than the MYSQL shown above...