select price,`date`
from a_price t
where not exists(select 1 from a_price where price<t.price)

------解决方案--------------------
SQL code
select price,`date` from  a_price order by price limit 1

------解决方案--------------------
探讨

SQL code
select price,`date`
from a_price t
where not exists(select 1 from a_price where price<t.price)