PHP MySQL Linking Posts to Users - php

Question

I decided to open a new question for this topic, as I have been having issues with it. My blog has a mysql database with the table posts complete with a post_user field. Each user has a form and can submit a post to a public blog. Once they submit this form, complete with a title and a body, when it is posted on the blog it should say by Username. My idea is that I can save the username to the post_user in the database upon form submission using $_SESSION info, but I am not exactly sure how to do this. Any help would be greatly appreciated.
The form, with the old UNSECURE way of entering the session author, note I am only including session data in the form to display what I am trying to show on a blog post, I don't know how to do it any other way hence my question:
<form action="" method="post">
<p>
<input type="hidden" name="user" id="user" value="<?php echo $_SESSION['user']['username'] ?>" readonly />
</p>
<p>
<input type="hidden" name="userid" id="userid" value="<?php echo $_SESSION['user']['id'] ?>" readonly />
</p>
<p>
<label for="title">Title: </label>
<input type="text" name="title" id="title" />
</p>
<p>
<textarea name="body" rows="20" cols="60"></textarea>
</p>
<p>
<input type="submit" value="Add Post" />
</p>
</form>
Code that posts the entry:
$posts = get_posts();
foreach($posts as $post)
{
?>
<h2><?php echo $post['title']; ?></h2>
<h4>By <font color="#FF6347"><?php echo $post['user']; ?></a></font> on <?php echo $post['date']; ?></h4>
<h4><?php echo $post['total_comments']; ?> comments, last comment <?php echo $post['last_comment']; ?>
<hr />
<p><?php echo $post['preview']; ?></p>
<?php
}
?>

Answer 1

You shouldn't save the username on the posts table. You should have two separate tables: one for the posts and one for the users, which are linked via a user_id field, a.k.a foreign key.
This is the way relational databases, such as MySQL, operate. This serves a few purposes:
You avoid repetition in case of one to many relations, which is exactly your case: one user can post many posts.
You use a unique identifier.
The information is organised better instead of mixing data together.
The way to tie the tables together when retrieving data is by using a JOIN statement, which links the two tables via the common user_id field. It is highly recommended to make this field an index, which would significantly speed up data retrieval. (Think about the difference between finding a certain word or sentence in a book by scanning through each and every page, and finding a chapter using the, well, index)
To sum up, you should have an id key in your $_SESSION super-global array, which you then insert to the user_id field upon post submission.
As for your question, you don't need to send the session data with a hidden input field, because it will be available even after submission - after all this is what session is all about. So why convert it to $_POST and expose it publicly?