Use Atlantic;
GO
SELECT  O.customer_id AS cust_id
, O.orders_id
, O.orders_sell_price AS sell_price
, O.orders_qty AS qty
, (O.orders_sell_price * O.orders_qty) AS line_total
, COUNT(*) OVER( ORDER BY customer_id) as nbr_orders
, SUM(orders_sell_price * O.orders_qty) OVER( ORDER BY customer_id) as cust_sales
FROM Orders AS O
ORDER BY customer_id