Edit / Update Query - Change Current Sales Information For A Specific Product

I am currently working on a website that deals with sales of products. For one of my pages for the website I need it to be able to change the current sales information for a specific product.

The top part of the following code selects the specific product however I cannot get the update query to work.

Code:
$describeQuery = "SELECT p.ID, p.NAME, dt.[Year], dt.[Month], dt.SalesVolume FROM Products p
join
(select ProductCode, sum(SalesVolume) as SalesVolume, [Year], [Month] from MonthlySales
group by ProductCode, [Year], [Month])dt
on dt.ProductCode = p.ID WHERE [NAME] = '$desiredProduct' AND [Year] = '$desiredYear' AND [Month] = '$desiredMonth'";

$editQuery = "UPDATE MonthlySales SET SalesVolume = '$NewSales' WHERE ID = '$desiredProduct' AND Year = '$desiredYear' AND Month = '$desiredMonth'";

$query = sqlsrv_query($link, $describeQuery);