sql数据库查询每个料号的第一笔明细

数据库sql查询每个料号的最早的采购单明细，要每个料号都能查询到

select buypn,buyid,buydate,buyitem,buyprice,buycurrency from (
select buypn,buyid,buydate,buyitem,buyprice,buycurrency,
row_number() over(partition by buypn order by buydate asc) rn
from buy_file
) t  where rn = 1

SELECT xx.* FROM
(
SELECT

FROM 表名
ORDER BY 采购日期 ASC
)xx
GROUP BY xx.料号
ORDER BY xx.采购日期DESC

select a.* 
from buy_file a
left join (select buypn
min(buydate)
from buy_file
group by buypn) b
on a.buypn = b.buypn and a.buydate = b.buydate
order by a.buypn