sql server 2005中的分区函数用法(partition by 字段)

分组取TOP数据是T-SQL中的常用查询， 如学生信息管理系统中取出每个学科前3名的学生。这种查询在SQL Server 2005之前，写起来很繁琐，需要用到临时表关联查询才能取到。SQL Server 2005后之后，引入了row_number()函数，row_number()函数的分组排序功能使这种操作变得非常简单。

create database StudentDB
go

use StudentDB
go

create table Student  --学生成绩表
(
 id int,  --主键
 Grade int, --班级
 Score int --分数
)
go

insert Student 
    select 1,1,88
union all select 2,1,66
union all select 3,1,75
union all select 4,2,30
union all select 5,2,70
union all select 6,2,80
union all select 7,2,60
union all select 8,3,90
union all select 9,3,70
union all select 10,3,80

go

--所有学生信息
select * from Student

id          Grade       Score
----------- ----------- -----------
1           1           88
2           1           66
3           1           75
4           2           30
5           2           70
6           2           80
7           2           60
8           3           90
9           3           70
10          3           80

(10 行受影响)

--不分班按学生成绩排名
select *,ROW_NUMBER() over(order by Score desc) as Sequence from Student

id          Grade       Score       Sequence
----------- ----------- ----------- --------------------
8           3           90          1
1           1           88          2
6           2           80          3
10          3           80          4
3           1           75          5
9           3           70          6
5           2           70          7
2           1           66          8
7           2           60          9
4           2           30          10

(10 行受影响)

--分班后按学生成绩排名
select *,row_number() over(partition by Grade order by Score desc) as Sequence from Student

id          Grade       Score       Sequence
----------- ----------- ----------- --------------------
1           1           88          1
3           1           75          2
2           1           66          3
6           2           80          1
5           2           70          2
7           2           60          3
4           2           30          4
8           3           90          1
10          3           80          2
9           3           70          3

(10 行受影响)