Retrieve New Data Only From Database - php

Question

I am developing an android Application that stimulates a poll notification feature. Therefore, I Created a service that keeps asking the server for the new data. However, I've used a table in my database called Seen. This table is used to be asked by the server for a specific user_id and if the news_id didn't exists in that table it will produce a notification.
The problem is when i launch the application for the first time. It retrieves all the data from the database because the server considering the users didn't see the news.
If Anyone Can Help me?
I Thought to solve it by this Idea: when I launch the application for the first time. Insert in seen table all of the news with that user_id in order to get 0 new messages. But i think it will be Not efficient.
This is my Database and my PHP script
Users table
User_ID | User_Name
--------------------
1 | John
2 | Carl
3 | Tomas
4 | Adam
5 | Nancy
News Table
News_ID | News_Text | news_date
---------------------------
1 | Hello World | CURRENTDATE()
2 | This is My car | CURRENTDATE()
3 | I had Ate pizza| CURRENTDATE()
4 | Leave Me Alone | CURRENTDATE()
5 | C++ Programming| CURRENTDATE()
Seen Table
ID | User_Id | News_Id
---------------------------
1 | 1 | 2
2 | 1 | 3
3 | 4 | 1
4 | 5 | 3
5 | 1 | 4
This is my PHP Code and it also showing my Query to get the news that didn't show in the Seen_news Table :
<?php
require('config.php');
$conn = mysqli_connect($servername, $username, $password, $db);
$query="SELECT * FROM news WHERE news_id NOT IN (SELECT news_id FROM news_seen WHERE user_id = '".$_GET['id']."')";
$result = mysqli_query($conn,$query);
$rows = array();
echo mysqli_error($conn);
while($row = mysqli_fetch_assoc($result)) {
$rows[] = $row;
}
echo json_encode($rows);
?>
Supposing that i am sending the User_Id to the PHP script and based on the result Query will show json file.

Answer 1

If you can add a create_date column to your Users table, you can select where Seen news_date is greater than User create_date.
Something like:
"SELECT * FROM news WHERE news_id NOT IN (SELECT news_id FROM news_seen WHERE user_id = '".$_GET['id']."') AND news_date > (SELECT create_date FROM user WHERE user_id = '".$_GET['id']."')"