mysql实现分组查询每个班级的前三名

1、创建表

drop table student;
create table student(
	id varchar(20),-- 编号
	class varchar(20),-- 年级
	score int-- 分数
);

2、创建测试数据

delete from student;
insert student values('1','一年级',82);
insert student values('2','一年级',95);
insert student values('3','一年级',82);
insert student values('4','一年级',40);
insert student values('5','一年级',20);
insert student values('6','二年级',95);
insert student values('7','二年级',40);
insert student values('8','二年级',3);
insert student values('9','二年级',60);
insert student values('10','二年级',10);
insert student values('11','三年级',70);
insert student values('12','三年级',60);
insert student values('13','三年级',40);
insert student values('14','三年级',90);
insert student values('15','三年级',20);

3、查询每个班级的前三名

select a.class,a.score 
from student a 
where (select count(*) from student where class=a.class and a.score<score)<3
order by a.class,a.score desc;