用SQL SERVER取分组数据第一条：查出每个班级的成绩第一名

create table test
(id int,
name varchar(10),
score int,
classname varchar(20));
 
insert into test values (1,'张三',100,'一班');
insert into test values (2,'李四',89,'一班');
insert into test values (3,'王五',97,'一班');
insert into test values (4,'赵六',87,'二班');
insert into test values (5,'孙七',94,'二班');
insert into test values (6,'杨八',76,'二班');

select t.* from
(select test.*,row_number() over (partition by classname order by score desc) rn 
from test) t
where rn=1;