select t1.a,t1.b,t1.c from table t1 join 
(select a,max(b) as maxDate from table group by a) t2
on t1.a=t2.a and t1.b=t2.maxDate

------解决方案--------------------
SQL code
select  * from tb t where 字段b=(select max(字段b) from tb where 字段a=t.字段a)

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

select t.字段a,t.字段b,t.字段c
from
(select row_number() over(partition by 字段a order by 字段b desc) rn,
字段a,字段b,字段c from tab) t
where t.rn=1

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

select * from table a
where not exists(select 1 from table b where a.字段a=b.字段b and a.字段b<b.字段b )

------解决方案--------------------
select * from table where b in(select max(b) from table group by a)