Customers

SELECT email FROM customer_entity as ce JOIN newsletter_subscriber as ns ON ns.subscriber_email = ce.email AND ns.subscriber_status = 1 JOIN sales_flat_order as sfo ON sfo.customer_id = ce.entity_id JOIN sales_flat_order_item as sfoi ON sfo.entity_id = sfoi.order_id JOIN catalog_product_entity as cpe ON cpe.entity_id = sfoi.product_id WHERE cpe.sku !='' group by ce.email;