Mysql DB麻烦

Question

I have this table that stores messages for the user. It has id(PK), username, message, time, date. When you log in to your account it shows a list of all of your chats. But this DB only shows the messages. Do I have to create another table somehow connected to the first DB or filter in a way that I get the usernames of the people I'm chatting with? What I mean by getting the usernames is that I have this list of the people I have messaged. Is there a way I could get those usernames?

I am sorry if this is not clear. If you need more explanation, tell me right away. This problem is quite complex for me.

By the way, here is the code:

 <div id='messages'>
        <nav>
            <ul id=''>
                <?php 
                    $m = new mysqli('localhost', 'root', 'xamppprogram', 'blue_messenger');
                    if($m === FALSE){
                        include('./errordb2.php');
                        die();
                    }

                    $sql = "SELECT * FROM messages WHERE username='$username'";
                    $results = $m->query($sql);
                    if($results->num_rows > 0){
                        while($r = $results->fetch_assoc()){
                            // What to do here?
                        }
                    } else {
                        echo "No new messages.";
                    }
                ?>
            <ul>
        <nav>
    </div>
    <div id='chat-content'>

Answer 1

You could add another column on the table, like toUser that stores the name of the user you're chatting with. Then you can use a GROUP BY toUser condition in your sql. This would be the easiest solution, but as others have stated in the comments of the question, a relational database would be best.

You would be best to use a prepared statement since user input seems to be used here and would be open to an SQL injection.

References:

• https://en.wikipedia.org/wiki/Prepared_statement
• https://en.wikipedia.org/wiki/SQL_injection