select
CUSTOMER.CUST_CODE as CODE,
CUSTOMER.CUST_NAME as NAME,
-- 顧客毎の受注件数 → CNT
count(ORDER_NO) as CNT,
-- 顧客毎の受注金額合計 → TTL_AMT
sum(ORDER_AMNT) as TTL_AMT,
-- 顧客毎の１回あたりの平均受注金額 → AVG_AMT
round(sum(ORDER_AMNT)/count(ORDER_NO), 1) as AVG_AMT

from CUSTOMER
inner join ORDERS on CUSTOMER.CUST_CODE = ORDERS.CUST_CODE

where
ORDER_DATE between '2023-09-01' and '2023-09-30'

group by CUSTOMER.CUST_CODE, CUSTOMER.CUST_NAME

order by
-- 表示項目CNTの降順
CNT desc,
-- 表示項目AVG_AMTの降順
AVG_AMT desc,
-- 表示項目CODEの昇順
CODE asc