UPDATE SKU
SET STD_COST_PRICE = 
(SELECT GOODS.STD_COST_PRICE
FROM SKU
LEFT JOIN
(SELECT GOODS_CODE,ROUND(AVG(STD_COST_PRICE)) AVEPRICE
 FROM SKU
 GROUP BY GOODS_CODE) AS S
ON SKU.GOODS_CODE  = S.GOODS_CODE
LEFT JOIN GOODS
ON SKU.GOODS_CODE  = GOODS.GOODS_CODE
WHERE SKU.STD_COST_PRICE < S.AVEPRICE)