题解 | #大小写混乱时的筛选统计#

WITH
    t_tag_count AS (
        SELECT
            ei.tag,
            count(*) answer_cnt
        FROM
            exam_record er
            LEFT JOIN examination_info ei ON er.exam_id = ei.exam_id
        GROUP BY
            ei.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;