Confused why same Join won't work futher down page

Question

Before anyone comments, I'm learning PHP/MySQL so I am aware my code is subject to sql injection, once I have my system built my next step is learning about security, 1 step at a time... Now to my problem

I have a basic page that allows people to post like a forum, I have everything posting to the database correctly, when I view the topic page itself, I successfully JOINed the users table with topics to get the user information(username, avatar), but when I try the same code with topics changed to posts, I'm getting a Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in view_topic.php on line 36 error.

Here is the working code..

$id = $_GET['topic_id'];
$sql =  "SELECT users.user_id, users.username, users.profile, topics.topic_id, topics.category, topics.sub_category, topics.topic_data, 
           topics.posted_by, topics.posted, topics.view
    FROM `topics` 
    JOIN `users` on topics.posted_by = users.user_id WHERE topic_id='$id'";

Here is my posts code NOT WORKING

$sql2 = "SELECT users.user_id, users.username, users.profile, post_id, post_content, post_date, post_topic, post_by 
    FROM `posts`
    JOIN `users` on posts.posted_by = users.user_id WHERE post_topic='$id'";

Use `mysql_error();` and see what you get and you are using `$id` -> `$id = $_GET['topic_id'];` in the query without escaping or sanitizing, you it will be easy for any one to break your database in a minute — Mr. Alien, Jul 14 '13 at 13:58
Your second query says "post_by" in the select and posted_by in the join. If that helps. — Pete Scott, Jul 14 '13 at 13:58

score 0 · Accepted Answer · answered Jul 14 '13 at 14:53

0

Double check your field names, "post_by" appears to be the field, but you've joined "posted_by".

Also I'd suggest reading up on mysqli and injection prevention sooner rather than later, best to learn it right the first time in my opinion.

answered Jul 14 '13 at 14:53

user2542256

153
7

Confused why same Join won't work futher down page

1 Answers1