Trouble with a query

[Knouen]

I have categories and items within categories.  A category may be appended to another category via its parentID field in the database.  ParentID can be set to NULL for a top-level category.  However, since the output of this list is used in a form for selecting a category to delete, it must be restricted not only to those cats without any child categories, but also cats which have no items in them.  Unfortunately I have no idea how to do the query for that.  If you help me I will wash your car.  Ok, not really.  But I'd appreciate it.

mysql_connect(DB_HOST, DB_USER, DB_PASS) or die(mysql_error());
mysql_select_db(DB_NAME) or die(mysql_error());
$result = mysql_query("select * from cat") or die(mysql_error());
$row = mysql_fetch_array($result);

/* Output all categories as dropdown list. */
echo '<select name="category"><option value="0" selected>-Select-</option>';
foreach($row as $cat){
echo '<option value=\"'.$cat['id'].'\">'.$cat['name'].'</option>';
}
echo '</select></li>';

[fenway]

Sounds like you need a few joins to find leafs vs nodes.

[Knouen]

I don't know how to do that. 

[fenway]

I don't know how to do that. 

Use JOINs to see if there is anything links to a given category.