题解 | #大小写混乱时的筛选统计#

select t1.tag,t2.cnt 
from (
select e1.tag,count(*) as cnt 
from exam_record as e2 left join examination_info as e1 
on e1.exam_id = e2.exam_id group by e1.tag ) t1 
inner join 
(select e1.tag,count(*) as cnt 
from exam_record as e2 left join examination_info as e1 
on e1.exam_id = e2.exam_id group by e1.tag )  t2 
on upper(t1.tag) = t2.tag 
and t1.tag != t2.tag 
and t1.cnt <= 3