I'm trying to use the modified preorder tree traversal method as layed out in the excellent sitepoint article to retrieve a category tree with a count of items below each category.

So far I've come up with this query which is so very nearly there but only returns rows for categories that contain an item.

Code:
SELECT root.name, 
           root.category_id, 
           COUNT( items.item_id ) AS item_count 
           FROM categories AS current, categories AS root, items 
           WHERE root.category_id != 1
                   AND ( current.lft BETWEEN root.lft AND root.rgt )
                   AND ( current.category_id = category_id ) 
           GROUP BY root.category_id 
           ORDER BY current.lft ASC
Can anybody help?

Many thanks