SQL & PL/SQL :: Find Count Of Customers Which Are In Same Campaign

The communication table has around 1 billion rows which is partitioned by a date column which is not used in the query. The hierarchy table has only 10000 rows. rewrite the query if its possible.Its trying to find the count of customers[distinct] which are in the same campaign.

select h.brand_cd, h.campaign_name, h.campaign_start_dt, h.campaign_name,h.campaign_desc,h.subject, count(distinct cc.customer_id)
from communication cc,hierarchy h
where cc.campaign_hierarchy_id = h.campaign_hierarchy_id
and h.brand_cd in ('ABY','AYO')
AND H.CAMPAIGN_OWNER = 'WONDER'
and h.campaign_start_dt >'1-JUL-2011'
group by h.brand_cd, h.campaign_name, h.campaign_start_dt, h.campaign_desc,h.subject;