要用满足完成数小于3的小写tag去匹配对应大写tag的数量！！！醉了 
select t1.tag,t2.answer_cnt
from (
            select tag 
            from exam_record t1
            join examination_info t2
            on t1.exam_id = t2.exam_id
            where upper(tag) <> tag
            group by tag
            having count(1) < 3
    ) t1
join  (
        select tag,count(1) as answer_cnt
        from exam_record t1
        join examination_info t2
        on t1.exam_id = t2.exam_id
        group by tag
        ) t2
on upper(t1.tag) = t2.tag
order by answer_cnt desc