How to only fetch only the new row from MySql automatically? - php

Question

I am making a messaging service for my users. I used AJAX for sending the message without refreshing the message. I want to fetch the new row from the database automatically (if the current user or the other side user enters any message), without refreshing the older messages.
<div id="readmsg">
#The messages is to be read here....
</div>
<textarea placeholder="Write your message.." id="msg"></textarea>
<input type="submit" value="Send" id="sendmsg">
<?php $user1 = 1; $user2 = 2; ?>
<script type="text/javascript">
$(document).ready(function(){
$("#sendmsg").on("click",function(e){
e.preventDefault();
var usera = <?php echo $user1.";";?>
var userb = <?php echo $user2.";";?>
var msg = $("#msg").val();
$.ajax({
url : "sendmessageprocess.php",
type : "POST",
data : {message:msg, user1:usera, user2:userb},
success : function(data){
document.getElementById("msg").value="";
$("#msg").val("");
}
});
})
});
</script>

Answer 1

As I see in comments the friends only complicated your problem and be far from your main problem
as a chatroom creator in past, I will seriously offer you to use another technologies instead of ajax
But if it's necessary to use ajax, the best way for solving your problem is:
after fetching new messages in your query, put the last row id in a some index in sessions or cookies such as:
$_SESSION['last_msg_id'] = $row['id'];
and in another requests get the messages that their ids is more than your last_msg_id
$query = 'SELECT * FROM `messages` WHERE `id` > "' . $_SESSION['last_msg_id'] . '"';
and, for new clients that haven't your session index get last 10 messages for example and create your session index by the told way. example:
if(isset($_SESSION['last_msg_id'])){
$query = 'SELECT * FROM `messages` WHERE `id` > "' . $_SESSION['last_msg_id'] . '"';
}else{
$query = 'SELECT * FROM `messages` ORDER BY `id` ASC LIMIT 10';
}
// your query process
$rows = {your rows};
foreach($rows as $row){
$_SESSION['last_msg_id'] = $row['id'];
}
// or
$rows = {your rows};
$last_row = end($row);
$_SESSION['last_msg_id'] = $last_row['id']