select 班级号,count(*) from 学生表 group by 班级号 不知道您的表是什么样的

select * from 班级 a left join (select 班级id,count(*) as counta from 学生 group by 班级id) b on a.班级id=b.班级id where b.counta=(select top 1 COUNT(*) as counta from StudioNews group by UserID order by counta desc) 可能存在人数最多的不止一个班级