MySQL 分组排序问题

SQL好久不写了，有些生疏了，一个分组排序问题想了快半天，整理下。

学生表

CREATE TABLE `t_student` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `name` varchar(128) DEFAULT NULL COMMENT '学生名称',
  `score` varchar(128) DEFAULT NULL COMMENT '分数',
  `class_id` varchar(128) DEFAULT NULL COMMENT '班级ID',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='学生表';

班级表

CREATE TABLE `t_class` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `name` varchar(128) DEFAULT NULL COMMENT '班级名称',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='班级表';

问题：查询出每个班级前三名的信息？

首先，如何查询每个班级前三名的SQL呢？

select * from t_student a
where (select count(1) from t_student where class_id = a.class_id and id <> a.id and score > a.score) < 3

完整SQL如下

select b.name,b.score,c.name from t_student b
join t_class c on b.class_id=c.id
where b.id in 
(select id from t_student a
where (select count(1) from t_student where class_id = a.class_id and id <> a.id and score > a.score) < 3)
group by b.class_id,b.id
order by b.class_id ,score desc;