oracle不使用group by 分组过滤数据

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() O外狒芙梨VER (PARTITION BY t.useridORDER BY t.createtime DES潮贾篡绐C) AS rn, t.* FROM t_book t)WHERE rn = 1