hive取不同班级前三名问题

1.hive只支持from里的子查询。

1.通过开窗函数实现

ROW_NUMBER() OVER 顺序排序。

RANK() OVER 跳跃排序，如果有两个第一级别时，接下来是第三级别。

DENSE_RANK() OVER  连续排序，如果有两个第一级别时，接下来是第二级别。

select * from 
(select 
   a.math
   ,studentid
   ,a.classid
   ,row_number() over(partition by a.classid order by math desc) t1
  
 from zxw_student_scores a) px
 where t1<=3
   ;

 

 

select * from 
(select 
   a.math
   ,studentid
   ,a.classid
   ,DENSE_RANK() over(partition by a.classid order by math desc) t1
  
 from zxw_student_scores a) px
 where t1<=3
   ;

 

select a.id,a.subject_id,a.student_id,a.score from score as a left join score as b on a.subject_id=b.subject_id and a.score>=b.score
group by a.subject_id,a.student_id,a.score
having count(a.subject_id)>=4
order by a.subject_id,a.score desc;