select * from tb t where price=(select min(price) from tb where cardid=t.cardid)

------解决方案--------------------
SQL code

DELETE  a
FROM    你的表名 a
WHERE   EXISTS ( SELECT TOP 1
                        *
                 FROM   你的表名
                 WHERE  cardId = a.cardId
                        AND price > a.price )

------解决方案--------------------
SQL code

create table dashanliu
(cardId char(5), price decimal(3,1), name char(5))

insert into dashanliu
select '001', 0.9, 'aaa' union all
select '002', 1.5, 'bbb' union all
select '001', 0.5, 'ccc' union all
select '003', 1.2, 'ddd'


select cardId,price,name
from
(select row_number() over(partition by cardId order by price) rn,
cardId,price,name from dashanliu) t
where t.rn=1

cardId price                                   name
------ --------------------------------------- -----
001    0.5                                     ccc  
002    1.5                                     bbb  
003    1.2                                     ddd