Mysql Public User chat to friend chat - php

Question

I currently followed a tutorial for a public user chat where it uses Msg_ID, Sender, Message. Sender being the name. I currently have a friend table where:
ID, my_id, friend_id.
But am unsure how to alter the chat so it's only sent to the recipient vice versa. And I have changed the chat table to the following: Msg_id, Author_id, Recipient_id, Message.
The current query for the chat is:
<?php
function get_msg() {
$query = "SELECT `Author_ID`, `Message` FROM `pdo_ret`.`chat` ORDER BY `Msg_ID` ASC";
$run = mysql_query($query);
$messages = array();
while($message = mysql_fetch_assoc($run)) {
$messages[] = array('Author_ID'=>$message['Author_ID'],
'message'=>$message['Message']);
}
return $messages;
}
function send_msg($Author_ID, $message) {
if(!empty($Author_ID) && !empty($message)) {
$Author_ID = mysql_real_escape_string($Author_ID);
$message = mysql_real_escape_string($message);
$query = "INSERT INTO `pdo_ret`.`chat` (Msg_ID, Author_ID, Message) VALUES (null, '{$Author_ID}', '$message')";
if($run = mysql_query($query)) {
return true;
} else {
return false;
}
} else {
return false;
}
}
?>
While the form for the chat is:
<form action="#" method="post" onsubmit="return InsertDefaultValues()" id="form_input">
<input hidden type="text" name="Author_ID" id="Author_ID"/>
<input hidden type="text" name="friend_id" id="friend_id"/>
<input type="text" id="message" cols="5" rows="4"></textarea>
<input type="submit" name="send" onsubmit="return InsertDefaultValues()" id="send" value="Send Message"/>
</form>
Here is my script for the session which I'm trying to use to define the user that is logged in.
<?php
session_start();
if(!isset($_SESSION["user"]) or !is_array($_SESSION["user"]) or empty($_SESSION["user"]));
?>

Answer 1

The following changes should be done to the queries:
Retrieve only your messages:
$query = "SELECT `Author_ID`, `Message` FROM `pdo_ret`.`chat` WHERE Recipient_id = '$Recipient_id' ORDER BY `Msg_ID` ASC";
Specify the recipent:
$query = "INSERT INTO `pdo_ret`.`chat` (Msg_ID, Author_ID, Recipient_id, Message) VALUES (null, '{$Author_ID}', '$Recipient_id', '$message')";

Answer 2

<?php
session_start();
if(!isset($_SESSION["user"]) or !is_array($_SESSION["user"]) or empty($_SESSION["user"]));
?>