Showing Selected Parent

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In my CMS, I have parent and children categories in one level and in one table (id, name, subcat). 

 

What i would like to do is, in PHP of course:

 

Upon editing a category, in a dropdown box, show selected, the parent of the category.  if there is no parent, show selected, a message saying "Not a subcategory".  In the selection though, still shows the parent options as possible selections.

 

Example:

Upon creating a new category, by default not a subcategory:

<select name="subcat" id="subcat">
   <option value="0" selected="selected">not a sub category</option>
   <option value="1">catOne</option>
   <option value="2">catTwo</option>
   <option value="4">catThree</option>
   <option value="8">catFour</option>
</select>

 

Upon editing a category, say a subcategory whose parent is "catTwo", should reflect the parent:

<select name="subcat" id="subcat">
   <option value="0">not a sub category</option>
   <option value="1">catOne</option>
   <option value="2" selected="selected">catTwo</option>
   <option value="4">catThree</option>
   <option value="8">catFour</option>
</select>

 

When a user clicks on the category they wish to edit becomes the $categoryid = the category's primary id. An example in relation to the select options above would be index.php?action=edit_category&id=3 (3 being a subcat and 1 being the parent, referencing the above)

 

The categories table looks like this:

 

id  name		description 	subcat
1  	catOne  	Parent One  	0
2 	catTwo 		Parent Two 		0
3 	subOne 		Child One		1
4 	catThree 	Parent Three	0
5 	subTwo 		Child Two		1
6 	subThree 	Child Three		4
7 	subFour 	Child Four		2
8 	catFour 	Parent Four		0

 

A new category screen is shown as an example of the setup:

 

The code I have so far is below.  It shows the parent category list in a dropdown box.  The add category dropdown is fine, but the edit dropdown is the problem.  I did not write all of this code below, just an fyi

 

// LISTS CATEGORIES
function category_list($var) {
if (isset($_GET['id']) && is_numeric($_GET['id']) && !is_null($_GET['id'])) { // Edit the category
	$categoryid = $_GET['id'];
	echo '<select name="subcat" id="subcat">';
                // Editing code is here....
                // Show "not a subcategory" and parents
                // Selected option is defined based on $categoryid
                // $categoryid = parent (0) then is is not a subcategory
                // $categoryid = subcat (>0) then show the parent selection
	echo '</select>';					
} else { // Add new category
	echo '<select name="subcat" id="subcat">';
   		$query = 'SELECT * FROM '.db('prefix').'categories WHERE subcat = 0';
   		isset($var) ? $query .= ' AND id <> $var' : $query .= '';
   		$result = mysql_query($query);
   		echo '<option value="0"';
   		!isset($var) ? print ' selected="selected">' : print '>';
   		echo 'not a sub category</option>';
   		while ($r = mysql_fetch_array($result)) {
     		echo '<option value="'.$r['id'].'"';
      		isset($var) ? print ' selected="selected">' : print '>';
      		echo $r['name'].'</option>';
   		}
	echo '</select>';
}
}

 

Can anyone help show me the right direction I need to go with this?  Do I need a join in my sql or do I need multiple sql queries? Moreso, how do I accomplish this after the query is completed?  I am not sure how to go about this...

 

Thanks for any and all help!!

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Should I have not said thank you so quickly?