Here is the code as it stands. This only returns a list that has values in the table_specs.
btw, my copy of Rudy's book was at home this weekend and I was at my girlfriends place all weekend so normally I would reference it for this type of problem.
, table_specs.id AS unique_spec_value
LEFT OUTER JOIN table_specs
ON table_list.id = table_specs.list_item_id
WHERE table_specs.inventory_item_id = 199