select item_id, buyer_id, sum(amt) as buyer_all_amt from A where where dt >= '20180701' and dt <= '20180930' and seller_id = 123  and  item_id in (select a.item_id from           (select item_id, sum(amt) as all_amt from A           where dt >= '20180701' and dt <= '20180930' and seller_id = 123            group by item_id            order by all_amt desc            limit 1)  a ) group by  item_id, buyer_id  order by buyer_all_amt desc limit 1