如何用SQL查询最近的正在进行或即将开始的团购列表？

<code class="sql">SELECT
    t4.*,
    NOW() AS '当前时间'  -- 添加当前时间列方便查看
FROM
(
    SELECT
        SUBSTRING_INDEX(SUBSTRING_INDEX(a.team_id_list, ',', b.help_topic_id + 1), ',', -1) AS team_id
    FROM
    (
        SELECT
            team_id_list
        FROM
        (
            SELECT
                GROUP_CONCAT(team_id) AS team_id_list
            FROM
                team_found
            WHERE
                team_start_time <= NOW() AND team_end_time > NOW()  -- 正在进行中的团购

            UNION ALL

            SELECT
                GROUP_CONCAT(team_id) AS team_id_list
            FROM
                team_found
            WHERE
                team_start_time > NOW()
            ORDER BY
                team_start_time ASC  -- 即将开始的团购，按开始时间升序排列
            LIMIT 1  -- 只取最近即将开始的一个团购
        ) t1
        WHERE
            t1.team_id_list IS NOT NULL
        LIMIT 1  -- 只取一个团购列表
    ) a
    JOIN mysql.help_topic b ON b.help_topic_id < (LENGTH(a.team_id_list) - LENGTH(REPLACE(a.team_id_list, ',', '')) + 1)
) t3
LEFT JOIN team_found t4 ON t3.team_id = t4.team_id;</code>