For example, if I try to ALTER the inline TVF I created above, I receive the following syntax error:

what-is-sql-cross-apply-6.sql

CREATE OR ALTER FUNCTION Sales.GetSalesByProduct
(
    @ProductID INT
)
RETURNS @SalesTable TABLE
(
    TotalSales MONEY
)
AS
BEGIN
	INSERT INTO @SalesTable (TotalSales)
	SELECT SUM (UnitPrice) AS TotalSales
	FROM Sales.SalesOrderDetail 
	WHERE ProductID = @ProductID
	GROUP BY ProductID

	RETURN
END;
GO