1 5 abc 2 6 bcd 1 7 ade 2 8 adc
若取按a列分组后,b列最大,的所有列的记录：
result a b c 1 6 bcd 2 8 adc
可以使用如下语句：
select * from test where b in (select max(id) from test group by a)
适用于所有数据库：
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
适用于所有数据库：
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
