UPDATE SKU
SET STD_COST_PRICE = (
    SELECT STD_COST_PRICE
    FROM GOODS
    WHERE GOODS.GOODS_CODE = SKU.GOODS_CODE
)
WHERE SKU_CODE IN (
    SELECT SKU_CODE
    FROM SKU a
    JOIN (
        SELECT GOODS_CODE, ROUND(AVG(STD_COST_PRICE), 1) AS av
        FROM SKU
        GROUP BY GOODS_CODE
    ) b
    ON a.GOODS_CODE = b.GOODS_CODE
    WHERE a.STD_COST_PRICE < b.av
)