Question

数据库计划： http://pastebin.com/aPXk1rMf

我想从“评论”表中选择“帖子所有者的 uName ”和“评论所有者的 uName ”（即我认为我需要cOwnerID＆gt; uName和pID＆gt ; uID＆gt; uName）以便我可以在发布评论后立即记录一些活动。我尝试使用MySQL连接以实现这一点，但我不能;所以这就是我徒劳的尝试。

$result = dbquery("INSERT INTO comments VALUES ('','$pID','$ownerID','$cmnt')"); // inserting a comment

$lastID = mysql_insert_id();

$res = dbquery("SELECT
                users.username AS username
            FROM `comments`
            LEFT JOIN `users` on comments.cOwnerID = users.uID
            WHERE (cID='$lastID')");

Answer 1

SELECT users1.username, users2.username FROM Posts p
WHERE p.pID="$POST_OF_INTEREST"
LEFT JOIN users users1 ON users1.uID=p.uID
LEFT OUTER JOIN comments ON comments.pID=p.pID
LEFT OUTER JOIN users users2 ON users2.uID=comments.cOwnerID

根据特定的帖子ID，这将获得发布者的用户名和评论该帖子的每个人的用户名（每条评论一行）。

Answer 2

我认为你必须为表用户使用别名，因为实际上，你将在这个表上有两个连接：一个用于帖子作者，另一个用于评论的作者。

尝试这样的事情：

            SELECT
                commentAuthor.username AS commentauthor_username,
                postAuthor.username AS postauthor_username
            FROM `comments`
            LEFT JOIN `users` AS commentAuthor on comments.cOwnerID = commentAuthor.uID
            LEFT JOIN `posts` on posts.pId = comments.pID
            LEFT JOIN `users` AS postAuthor on posts.uID = postAuthor.uID
            WHERE (cID='$lastID')

Answer 3

SELECT Users.uName  AS UserNamePost
             , UserComment.uName AS UserNameComment
FROM Users
INNER JOIN Posts
    ON Posts.uID = Users.uID;
INNER JOIN Comments
    ON Comments.pID  = Posts.pID ;
INNER JOIN Users AS UserComment
    ON Comments.cOwnerID   = UserComment.uID  ;

这样做的目的是让发布帖子的用户然后加入用户以获取帖子的所有评论

Answer 4

“SELECT users.username AS用户名， comments.cOwnerID AS commentOwner， users.uID AS userID 从评论 LEFT JOIN 用户上 commentOwner = userID 哪里 commentOwner ='{$ lastID}'';

使用多个mysql连接

4 个答案: