获取分组后取某字段最大一条记录
方法一：(效率最高)
select * from test as a
where typeindex = (select max()
from test as b
where = );
方法二：(效率次之)
select
a.* from test a,
(select type,max(typeindex) typeindex from test group by type) b
where = and = order by
方法三：
select a.* from test a inner join (select type , max(typeindex) typeindex from test group by type) b on = and = order by
方法四：(效率最低)
select * from
(
select *,ROW_NUMBER() OVER(PARTITION BY type ORDER BY typeindex DESC) as num
from test
) t
where = 1