mysql查询news表 查询CategoryId=2 以Classifid分组 求出每组最新的2条数据?

实现一：

SELECT
*
FROM
jiuding_news   main
WHERE
CategoryId=2
AND
( SELECT  COUNT(*)
FROM  jiuding_news   sub
WHERE   main.CategoryId  = sub.CategoryId
AND  main.Classifid= sub.Classifid
AND  main.id  <=  sub.id )  <=2

实现二：

select * from (

select *,(select count(*) from news where a.classifid=classifid and a.datetime<=datetime)rn
from news a where categoryid=2 
)t where rn<=2

：查询结果