1. 查询class_id情况分组情况
代码：1，形成临时表t1
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id;
2. 得出表t1的最大值：max=2
select max(t1.student_name)
from
(select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id) t1;
3. 查出最大值那一行的class_id，形成表临时表t2
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id
having count(1)>=
(select max(t1.student_name)
from(
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id) t1);
4. 得到此class_id
select t2.class_id
from(
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id
having count(1)>=
(
select max(t1.student_name)
from(
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id) t1)) t2;
5. 根据此class_id,查出此表的内class_id=1对应的内容
select u1.student_name,u1.class_id
from b_user_info u1
where u1.class_id=
(select t2.class_id
from(
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id
having count(1)>=(
select max(t1.student_name)
from(
select count(1) student_name ,u.class_id
from b_user_info u
group by u.class_id) t1)) t2)
;