SQL Server 2008中，选择学生成绩优异的学生，从每一类

Question

我有一个分贝，看起来像这样

+--------+-------+-------+ 
| ID  | Class | grade | 
+--------+-------+-------+ 
| 123 | A | 100 | 
| 2  | B | 84 | 
| 357 | A | 46 | 
| 43  | B | 12 | 
| 55677 | B | 78 | 
| 63432 | A | 63 | 
+--------+-------+-------+ 

很明显，我处理的更大分贝。 更多学生和更多课程 我想实现的是从每个班级中挑选两名成绩最高的学生。

所以，它应该显示：

+-------+-------+-------+ 
| ID | Class | Grade | 
+-------+-------+-------+ 
| 123 | A  | 100 | 
| 63432 | A  | 63 | 
| 2  | B  | 84 | 
| 55677 | B  | 78 | 
+-------+-------+-------+ 

如何做到这一点谢谢！

我尝试这样做，但它给了我所有行

select id, class, max(grade) 
from school 
group by id, class 

++++

有，我想这个数据库做另一件事。 我如何才能从每班上拉10％的学生？ 后，我加了一个等级的属性，我尝试使用这样的“具有”组后：

rank < count(distinct ID) * 0.05 

谢谢！

Answer 1

使用ROW_NUMBER()功能与分区的子句。

;WITH CTE AS (

SELECT id, Class, Grade, 
     ROW_NUMBER() OVER(PARTITION BY Class ORDER BY Grade DESC) as rnk 
FROM tableName 
) 

SELECT id, Class, Grade 
FROM CTE 
WHERE rnk <=2 

Answer 2

我认为，DENSE_RANK比ROW_NUMBER更好地在这里。

查询

;with cte as(
    select [rank] = dense_rank() over(
     partition by [Class] 
     order by [grade] desc 
    ), * 
    from [your_table_name] 
) 
select * from cte 
where [rank] <= 2; 

Answer 3

试试这个：

WITH result AS (

SELECT Id, Class, Grade, 
     dense_rank() OVER(PARTITION BY Class ORDER BY Grade DESC) as DenseRank 
FROM tableName 
) 

SELECT Id, Class, Grade 
FROM result 
WHERE DenseRank <=2 

多个学生用同一档次最高的也将予以考虑。

Answer 4

为此，你需要通过使用组，并具有：

select id,Class,Grade 
    from Student e 
    where Grade=(select max(Grade) 
    from Student w 
    group by w.Class having e.class=w.class)