Use Atlantic;
GO
SELECT Ord.customer_id
, (Ord.orders_qty * Ord.orders_sell_price) AS line_total
,	(SELECT CAST(AVG(O.orders_qty * O.orders_sell_price) AS DECIMAL(8,2))	
	FROM Orders AS O) AS avg_table_value
FROM  Orders AS Ord
ORDER BY Ord.customer_id;