I am having the following query and I am wondering how should I construct an index for each of the clients and products tables.

Code:
SELECT 
     clients.id AS id, 
     clients.name AS name, 
     COUNT(DISTINCT products.product_id) AS counts 
FROM 
     clients 
INNER JOIN 
     products ON (clients.id = products.client_id) 
WHERE 
     CAST("2008-07-30"
...