Row_number() OVER(PARTITION BY xxx ORDER BY XXX）分组排序

--//创建一个信息表
CREATE TABLE user_student(id decimal(18,0) identity(1,1),st_name nvarchar(30),class nvarchar(10),score decimal(18,2))
--//插入测试数据============start===================
insert into user_student(st_name,class,score)
values(‘张三‘,‘甲‘,‘90‘)

insert into user_student(st_name,class,score)
values(‘张四‘,‘甲‘,‘65‘)

insert into user_student(st_name,class,score)
values(‘张五‘,‘甲‘,‘88‘)

insert into user_student(st_name,class,score)
values(‘李三‘,‘乙‘,‘97‘)

insert into user_student(st_name,class,score)
values(‘李四‘,‘乙‘,‘88‘)

insert into user_student(st_name,class,score)
values(‘李五‘,‘乙‘,‘78‘)

insert into user_student(st_name,class,score)
values(‘王三‘,‘丙‘,‘86‘)

insert into user_student(st_name,class,score)
values(‘王四‘,‘丙‘,‘69‘)

insert into user_student(st_name,class,score)
values(‘王五‘,‘丙‘,‘59‘)
--//插入测试数据============end===================
select * from user_student

--//每个班级分数前两名的学生信息
SELECT ST_NAME,CLASS,SCORE
FROM (
SELECT Row_number() OVER(PARTITION BY CLASS ORDER BY SCORE DESC) AS NUM,*
FROM user_student
) AS T
WHERE NUM<=2

表内数据：                   输出结果：