题解 | 大小写混乱时的筛选统计

select用了个关联子查询（感觉好久没用了）

with t as (
    select tag,sum(count(*)) over w as answer_cnt,count(*) cnt
    from exam_record join examination_info using(exam_id)
    group by tag
    window w as (partition by upper(tag))
)
select t1.tag
    ,(select cnt from t as t2 where upper(t1.tag)=t2.tag) as answer_cnt
from t as t1
where answer_cnt-cnt>0 and cnt<3 and tag!=upper(tag)