从3个表中获取信息SQL&的PHP [英] Getting information from 3 tables SQL & PHP

问题描述

我正在使用HTML，CSS，PHP和MySQl创建类似系统的博客.该站点由三个表组成.

Im making a blog like system using HTML, CSS, PHP and MySQl. The site is made up of three tables.

用户( ID ，用户名，密码，电子邮件)
帖子( postid ，标题，帖子)
来自帖子的评论( postid ， id ，评论，commentid)postid和用户的id.

user (id, username, password, email)
posts (postid, title, post)
comments (postid, id, comment, commentid) postid coming from posts and id from user.

我正在尝试显示所有评论以及将其留给特定帖子的用户名.

I am trying to display all of the comments and the users username who left them for a certain post.

当我在phpmyadmin中使用此查询时:从user.id = comments.id上的用户INNER JOIN中选择user.username，comments.comment，其中postid = 1

When i use this query in phpmyadmin: SELECT user.username, comments.comment FROM user INNER JOIN comments on user.id=comments.id where postid=1

它显示了我的需要.

当我将其添加到php中时，我会得到一个空白页.

When i add it into php i get a blank page.

<?php
//echo "1";
session_start();

$connect = mysql_connect('localhost', 'root', 'root') or die("Couldn't connect");
mysql_select_db("com541blog") or die("Couldn't connect to database");

//echo "2";
//$postid = $_GET['type'];
$_SESSION['postid'] = $postid;

//echo "3";
$query_comments = mysql_query("SELECT user.username as username, comments.comment as comment     FROM user INNER JOIN comments on user.id=comments.id WHERE postid='1'");

$info = mysql_fetch_array($query_comments);

$username = $info['username'];
$comment = $info['comment'];

echo $username;                         
echo $comment;

?>

提前感谢您的帮助:)

Thanks in advance for the help :)

推荐答案

我怀疑您的第一行有错误，即在连接"末尾缺少"c".

Your first line has an error I suspect, ie missing 'c' near the end of 'connect'.

include("db_connet.php"); 应该是 include("db_connect.php");

此外，缺少分号; .这个:

Also, missing a semi-colon ;. This:

$query_comments = ("SELECT user.username, comments.comment 
                    FROM user INNER JOIN comments on user.id=comments.id 
                    where postid=1")

应阅读:

$query_comments = ("SELECT user.username, comments.comment 
                    FROM user INNER JOIN comments on user.id=comments.id 
                    where postid=1");

此外，在执行操作时，使用表名来限定每个列名也是不错的做法，例如， user.username .但是您可能更喜欢使用表别名的以下更简洁的语法:

Also, not bad practice to qualify each of your column names with a table name eg user.username as you're doing. But you might prefer eg the following more concise syntax using table aliases:

$query_comments = ("SELECT u.username, c.comment 
                    FROM user u INNER JOIN comments c on u.id = c.id 
                    where c.postid = 1");

(请注意，表别名不必是单个字母，因此可以方便地将表名称(例如"ManufacturerSuppliedPartsListData_Feb01")简化为"mpl"，而又不会失去其含义.您可以使用客户"和信用"，而不只是"c"，例如"cust"和"cred")

(Note the table aliases don't need to be a single letter, so can be handy reducing a table name such as "ManufacturerSuppliedPartsListData_Feb01", to eg "mpl", without losing their meaning. Or eg if you've got "Customers" and "Credit" instead of just "c" you might use eg "cust" and "cred")

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