mysql子查询错误未知列'；上一次'；在'；其中第'条；

当我使用mysql进行子查询时，在“where子句”中会出现未知列“tv.last_time”，我该怎么办？在执行子查询时，我希望使用外部条件筛选出不符合要求的记录

SELECT
    info_topic.*, b.newMessage
FROM
    info_topic
LEFT JOIN `info_topic_visit` AS tv ON tv.topic_id = info_topic.id
AND tv.user_id = 225
LEFT JOIN (
    SELECT
        p.topic_id,
        count(*) AS newMessage
    FROM
        info_post p
    WHERE
        p.create_time > tv.last_time
    GROUP BY
        p.topic_id
) AS b ON b.topic_id = info_topic.id
ORDER BY b.newMessage DESC

数据库架构：

---

子查询的问题是，

tv

别名在那里没有任何意义，因此无法引用该别名对应的表中的任何内容。一种方法是在select子句中将子查询转换为相关子查询：

SELECT
    i.*,
    (SELECT COUNT(*) FROM info_post p
     WHERE p.create_time > tv.last_time AND p.topic_id = i.id) AS newMessage
FROM info_topic i
LEFT JOIN info_topic_visit AS tv
    ON tv.topic_id = info_topic.id AND tv.user_id = 225
LEFT JOIN info_topic_member tm
    ON i.id = tm.topic_id AND
       tm.del_flag = 0    AND
       tm.apply_status = i.open_type AND
       tm.user_id = 225
WHERE
    i.del_flag = 0 AND
    i.id > 0       AND
    tm.id IS NOT NULL
ORDER BY
    newMessage DESC;

---

可能还有一种方法可以重新构造查询，这样您就不需要使用效率低下的相关子查询。

您可以将查询中使用的表的数据库架构与一些示例数据共享吗。还有，您想要的输出数据是什么。好的，我将简化它。您可能需要等待一点，看看是否有人可以做得更好。现在，你可以用这个。

SELECT
    i.*,
    (SELECT COUNT(*) FROM info_post p
     WHERE p.create_time > tv.last_time AND p.topic_id = i.id) AS newMessage
FROM info_topic i
LEFT JOIN info_topic_visit AS tv
    ON tv.topic_id = info_topic.id AND tv.user_id = 225
LEFT JOIN info_topic_member tm
    ON i.id = tm.topic_id AND
       tm.del_flag = 0    AND
       tm.apply_status = i.open_type AND
       tm.user_id = 225
WHERE
    i.del_flag = 0 AND
    i.id > 0       AND
    tm.id IS NOT NULL
ORDER BY
    newMessage DESC;