I understand, but I don't know how your chart.js code works. You want monthly sales? A query for that might look like:
SELECT CONCAT( LEFT(MONTHNAME(OrderDate), 3), ' ', YEAR(OrderDate)) AS XLABEL, SUM(OrderAmount) AS YVALUE, MONTH(OrderDate) AS TheMonth, YEAR(OrderDate) AS TheYear FROM ps4_orders GROUP BY CONCAT( LEFT(MONTHNAME(OrderDate), 3), ' ', YEAR(OrderDate)), YEAR(OrderDate), MONTH(OrderDate) ORDER BY YEAR(OrderDate), MONTH(OrderDate) ASC