题解 | #大小写混乱时的筛选统计#
大小写混乱时的筛选统计
https://www.nowcoder.com/practice/81cb12931a604811ae69d332515c7734
WITH t_tag_count as (
SELECT tag, COUNT(uid) as answer_cnt
FROM exam_record
LEFT JOIN examination_info USING(exam_id)
GROUP BY tag
)
select a.tag,b.answer_cnt
from t_tag_count as a
join
t_tag_count as b
on upper(a.tag) = b.tag and a.tag != b.tag and a.answer_cnt < 3
自连接的应用，先找到所有答题标签和次数，然后自连接两个表，按照要求找目标答案。
