error in sql query
			SELECT 
				products.*,
				catalog.name AS cat_name,
				SUM(orders_content.admin_price * orders_content.admin_quantity) AS product_amount,
				SUM(orders_content.admin_quantity) AS product_quantity
			FROM orders_content
			INNER JOIN orders ON orders.oid=orders_content.oid
			INNER JOIN products ON products.pid = orders_content.pid
			
			INNER JOIN catalog ON catalog.cid = products.cid
			WHERE 
				catalog.key_name <> 'gift_cert' AND
				products.is_visible='Yes' AND
				DATE_ADD(orders.create_date, INTERVAL 2 MONTH)>NOW() AND 
				orders.status='Completed' AND 
				orders.payment_status='Received' 
			GROUP BY orders_content.pid
			ORDER BY
				product_quantity DESC
			LIMIT 6
		
.mysql error : Duplicate entry '30' for key 1