SQL语句：按a列分组后b列最大的所有列记录

1 5 abc 
2 6 bcd 
1 7 ade 
2 8 adc

result a b c 
1 6 bcd 
2 8 adc

select * from test where b in (select max(id) from test group by a)

select   t1.a,t1.b,t1.c 
from   test   t1   
inner   join 
(seelct   a,max(b)   as   b   from   test   group   by   a)   t2   
on   t1.a=t2.a   and   t1.b=t2.b

select   a,b,c 
from( 
select   a,b,c 
,row_number()over(partition   by   a   order   by   b   desc)   rn 
from   test 
)   
where   rn=1