小编Mil*_*lic的帖子

我是 MySQL 编程新手，但有一个问题。我创建了这个查询：

SELECT *,
       topics.createdate AS TopicCreateDate,
       (SELECT (SELECT username
                FROM   users
                WHERE  id = topicanswers.userid)
        FROM   topicanswers
        WHERE  topicid = topics.id
        ORDER  BY id DESC
        LIMIT  1)        AS LastPost
FROM   topics
       INNER JOIN categories
               ON topics.categoryid = categories.id
       INNER JOIN users
               ON topics.userid = users.id
ORDER  BY topics.lastupdate DESC

此查询列出所有Topics、联接类别和用户，UserID以及类别 IDTopics和Username来自TopicAnswersas LastPost。它命令它们LastUpdate在Topics由 控制的范围内下降TRIGER。

它工作得很好，但是这个子查询有一个问题：

            (SELECT (SELECT username
                    FROM   users
                    WHERE  id …

当连接表中的记录不存在时，我如何连接两个表。我尝试过这样的事情：

SELECT 
    Confessions.ID, Confessions.WriteTitle, Confessions.WriteArea,
    Confessions.POST_DATE, Votes.Type
FROM Confessions LEFT OUTER JOIN Votes ON Confessions.ID = Votes.PostID 
WHERE ForUser = :ForUser AND Status = :Status AND Votes.IP_Check = :IP_Check

但是当来自带有 PostID 的投票记录（如 Confessions 中的 ID）不存在时，MySQL 会返回此记录的空结果。有没有其他办法？