目录
- 问题：
- SQL解答：
问题：
下面是某个班级的成绩表，需要筛选出每个科目前2名的学生信息。如果分数一样，名次是并列的，后面的同学名次就不连续。比如有2个同学是第一名，那么下一个同学的名次就是第3名，呈现1,1,3的名次排列。
stu_id stu_name subject score
1001 张三 语文 90
1001 张三 数学 80
1001 张三 英语 70
1002 李四 语文 90
1002 李四 数学 75
1002 李四 英语 80
1003 王五 语文 80
1003 王五 数学 70
1003 王五 英语 60
SQL解答：
非常典型的分组topN的问题，是面试经常被问到的。直接使用开窗函数排名即可，注意下row_number、rank、dense_rank三个开窗函数不同场景下的使用。
with temp as
(select 1001 as stu_id,'张三' as stu_name,'语文' as subject,90 as scoreunion allselect 1001 as stu_id,'张三' as stu_name,'数学' as subject,80 as scoreunion allselect 1001 as stu_id,'张三' as stu_name,'英语' as subject,70 as scoreunion allselect 1002 as stu_id,'李四' as stu_name,'语文' as subject,90 as scoreunion allselect 1002 as stu_id,'李四' as stu_name,'数学' as subject,75 as scoreunion allselect 1002 as stu_id,'李四' as stu_name,'英语' as subject,80 as scoreunion allselect 1003 as stu_id,'王五' as stu_name,'语文' as subject,80 as scoreunion allselect 1003 as stu_id,'王五' as stu_name,'数学' as subject,70 as scoreunion allselect 1003 as stu_id,'王五' as stu_name,'英语' as subject,60 as score
)
select
stu_id
,stu_name
,subject
,score
from
(select stu_id,stu_name,subject,score,rank() over(partition by subject order by score desc) as rkfrom temp
) t1
where rk<=2;---结果：
stu_id stu_name subject score
1001 张三 数学 80
1002 李四 数学 75
1002 李四 英语 80
1001 张三 英语 70
1001 张三 语文 90
1002 李四 语文 90
)
