improvements to query with hierarchical elements

Greetings,

I have a complex query which I am trying to figure out the most efficient
way of performing.

My database is laid out as follows:

items -have_many-> events -have_many-> event_locations -have_many->
locations

also rows in the location_links table link two locations together in a
parent-child relationship and rows in the location_descendants table provide
a full list of the descendants of a

particular location.

I am trying to find all locations which both are direct children of a given
parent location, and are associated with at least one item in a constrained
subset of items.

(eg. Find all states of the USA in which at least one wooden axe was made.
Also find the number of wooden axes made in each state.)

I have developed the following query:

SELECT locations.*,

location_ids.item_count AS item_count

FROM locations

JOIN

(SELECT immediate_descendants.ancestor_id AS id,

COUNT(DISTINCT creation_events.item_id) AS
item_count

FROM event_locations

JOIN

(SELECT *

FROM location_descendants

WHERE ancestor_id IN

(SELECT child_id

FROM location_links

WHERE parent_id = *note 1*

)

) AS immediate_descendants

ON event_locations.location_id =
immediate_descendants.descendant_id

JOIN

(SELECT *

FROM events

WHERE item_id IN (*note 2*) AND
association = 'creation'

) AS creation_events

ON event_locations.event_id =
creation_events.id

GROUP BY immediate_descendants.ancestor_id

) AS location_ids ON locations.id = location_ids.id

*note 1* - the id of the parent location.

*note 2* - the query which returns a list of constrained item ids

This works but I am looking for any way to improve the performance of the
query (including changing the layout of the tables). Any ideas, suggestions
or general pointers would be greatly appreciated.

Thanks very much,

Ryan