SELECT m, d, goods_id, sales, AVG(sales) OVER (PARTITION BY goods_id,m ORDER BY d ASC ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as sales_running_avg
FROM
(
SELECT
TD_TIME_FORMAT(time,'yyyy-MM-dd','JST') AS d, TD_TIME_FORMAT(time,'yyyy-MM','JST') AS m, goods_id, SUM(price*amount) AS sales
FROM sales_slip
WHERE TD_TIME_RANGE(time, '2013-01-01', '2013-02-01', 'JST')
GROUP BY TD_TIME_FORMAT(time,'yyyy-MM-dd','JST'), TD_TIME_FORMAT(time,'yyyy-MM','JST'), goods_id
) t
ORDER BY goods_id, m, d