[英]Difficulty with join 3 tables in a query in php
My database has 3 tables i wish to access in the select query but I cannot seem to get it to work. 我的数据库有3个表,我希望在select查询中访问这些表,但似乎无法正常工作。 Selecting from 2 tables works fine so I know everything else is working apart from my code for selecting from 3 tables. 从2个表中进行选择可以很好地工作,所以我知道除了从3个表中进行选择的代码以外,其他所有功能都在起作用。 My database has been created on PHPmyadmin 我的数据库已在PHPmyadmin上创建
The Tables are as follows: 表格如下:
forum_replies forum_replies
forum_topics forum_topics
users 用户
This is the code I have tried to use and shows the fields I wish to select: 这是我尝试使用的代码,并显示了我希望选择的字段:
$queryreply = "SELECT forum_replies.reply_id, forum_replies.topic_id, forum_replies.user_id,
forum_replies.reply_text, forum_replies.reply_date, users.user_id, users.username
forum_topics.topic_id,forum_topics.topic_title, forum_topics.topic_date
FROM forum_replies
JOIN forum_topics
ON forum_replies.topic_id = forum_topics.topic_id
JOIN users
ON forum_replies.user_id = users.user_id
";
$result = mysql_query($queryreply) or die (mysql_error());
$row = mysql_fetch_array($result);
Example in code would be appreciated. 代码示例。 Thanks 谢谢
You miss the ,
after users.username
.. 你错过了,
以后users.username
..
SELECT forum_replies.reply_id, forum_replies.topic_id, forum_replies.user_id,
forum_replies.reply_text, forum_replies.reply_date, users.user_id, users.username,
forum_topics.topic_id,forum_topics.topic_title, forum_topics.topic_date
Use this query: 使用此查询:
SELECT a.reply_text, a.reply_date, b.topic_title, c.username
FROM forum_replies a
LEFT JOIN forum_topics b ON a.topic_id=b.topic_id
LEFT JOIN users c ON a.user_id=c.user_id
// apply WHERE, ORDER, GROUP if needed
Apart from syntax errors, you should use LEFT JOIN
and table alias in your case. 除语法错误外,您还应使用LEFT JOIN
和表别名。
To show also the topic creator's username, you can adjust the query to the following: 要同时显示主题创建者的用户名,您可以将查询调整为以下内容:
SELECT a.reply_text, a.reply_date, b.topic_title, c.username AS reply_user, (SELECT username FROM users WHERE user_id=b.user_id) AS topic_creator
FROM forum_replies a
LEFT JOIN forum_topics b ON a.topic_id=b.topic_id
LEFT JOIN users c ON a.user_id=c.user_id
// apply WHERE, ORDER, GROUP if needed
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