oracle不使用group by 分组过滤数据

1、1.userid是分组列

2、createtime是排序列

3、查询以userid分组,以createtime排序,每组的第一条记录

4、SELECT *

FROM (

    SELECT ROW_NUMBER() OVER (PARTITION BY t.userid ORDER BY t.createtime DESC) AS rn, t.*

    FROM t_book t

)

WHERE rn = 1