Actually this is a better sql query
SELECT
YEAR(MTIT_DATE) as SalesYear,
MONTH(MTIT_DATE) as SalesMonth,
SUM(MTIT_QTY) AS TotalSales
FROM INVTXN WHERE MTIT_DATE >= '2013-01-01' and MTIT_DATE <= '2013-12-31' AND MTIT_CODE = 'PART ID HERE' AND MTIT_TYPE = 'S'
GROUP BY YEAR(MTIT_DATE), MONTH(MTIT_DATE)
ORDER BY YEAR(MTIT_DATE), MONTH(MTIT_DATE);
Kelloggs