Why is my code not working?

I copied the code exactly like the lecture video.

I'm getting error 1055: "Expression #1 of SELECT list is not in GROUP BY clause and contains..."

CREATE TEMPORARY TABLE DEMAND_SUPPLY

SELECT

OH.CUSTOMER\_ID,

OI.PRODUCT_ID,

PRODUCT_DESC,

OH.ORDER_ID,

PC.PRODUCT_CLASS_DESC,

SUM(OI.PRODUCT_QUANTITY) AS DEMAND,

CEIL(SUM(OI.PRODUCT_QUANTITY) + (SUM(OI.PRODUCT_QUANTITY)*0.25)) AS NEW_DEMAND,

PRODUCT_QUANTITY_AVAIL AS SUPPLY,

ROUND(PRODUCT_QUANTITY_AVAIL/SUM(PRODUCT_QUANTITY),2) AS CURRENT_RATIO,

ROUND(PRODUCT_QUANTITY_AVAIL/CEIL(SUM(OI.PRODUCT_QUANTITY) + (SUM(OI.PRODUCT_QUANTITY)*0.25)),2) AS NEW_RATIO

FROM ORDER_HEADER OH

JOIN ORDER_ITEMS OI USING(ORDER_ID)

JOIN PRODUCT USING(PRODUCT_ID)

JOIN PRODUCT_CLASS PC ON PC.PRODUCT_CLASS_CODE = PRODUCT.PRODUCT_CLASS_CODE

GROUP BY PRODUCT_ID