Notification for user group - php

Question

I'm working on a event manager and I would like to create a notification system for a group of users.
When an admin creates a new event then php create a notification inside mysql with status 0 if not read and then it changes to status 1 if read.
The problem is that I'm using the group id instead of the user id, and when the first logged user click on the notification it updates the notification status so other users are not viewing the notification. Maybe inserting a row for each user into the database can solve this problem? do I need to use an array of user's ids?
This is what i've done so far:
session_start();
// admin id
$userid = $_SESSION['user_id'];
include('../../../config/database.php');
$event_title = $_POST['titleevent'];
$event_color = $_POST['eventcolor'];
$event_start = $_POST['startevent'];
$new_start_date = date('Y-m-d 00:00:00', strtotime($event_start));
$event_end = $_POST['endevent'];
$new_end_date = date('Y-m-d 23:59:00', strtotime($event_end));
$event_group = $_POST['usergroup'];
$event_description = $_POST['eventdescription'];
if ($create_event = mysqli_prepare($conn, "INSERT INTO user_events (event_title, event_description, event_start, event_end, event_color, event_group)
VALUES (?, ?, ?, ?, ?, ?)" )) {
mysqli_stmt_bind_param($create_event, 'sssssi', $event_title, $event_description, $new_start_date, $new_end_date, $event_color, $event_group);
mysqli_stmt_execute($create_event);
// get event id
$event_id = mysqli_insert_id($conn);
$event_start_date = date('d-m-Y', strtotime($new_start_date));
$notification = "Nuovo evento <span class='text-warning'><strong>$event_title</strong></span> inizia il $event_start_date";
$notification_status = "0";
$notification_category= "events";
$event_notification = mysqli_prepare($conn, "INSERT INTO event_notifications (e_notification_sent_by, e_notification_sent_to, e_notification_message, e_notification_time, e_notification_status, e_notification_category, e_notification_category_id) VALUES(?,?,?,now(),?,?,?)");
mysqli_stmt_bind_param($event_notification, 'iisisi', $userid, $event_group, $notification, $notification_status, $notification_category, $event_id);
mysqli_stmt_execute($event_notification);
mysqli_stmt_close($event_notification);
echo "event created";
mysqli_stmt_close($create_event);
}else{
echo "Ops, error";
}
Many thanks for you help
UPDATE i've managed to make it working using an array and foreach in this way:
$event_start_date = date('d-m-Y', strtotime($new_start_date));
$notification = "Nuovo evento <span class='text-warning'><strong>$event_title</strong></span> inizia il $event_start_date";
$notification_status = "0";
$notification_category= "events";
$sql = "SELECT user_join_id FROM user_group_join WHERE group_join_id='$event_group'";
$result= mysqli_query($conn,$sql);
$datas= array();
if(mysqli_num_rows($result) > 0){
while($row=mysqli_fetch_array($result, MYSQLI_ASSOC)){
$datas[]= $row;
}
}
foreach($datas as $data) {
$id_cliente = $data['user_join_id'];
$event_notification = mysqli_prepare($conn, "INSERT INTO user_notifications (notification_sent_by, notification_sent_to, notification_message, notification_time, notification_status, notification_category, notification_category_id) VALUES(?,?,?,now(),?,?,?)");
mysqli_stmt_bind_param($event_notification, 'iisisi', $userid, $id_cliente, $notification, $notification_status, $notification_category, $event_id);
mysqli_stmt_execute($event_notification);
mysqli_stmt_close($event_notification);
}
Now the question is how can i can i convert it with a prepared statement? And also it looks like i'm going to use a lot of server resources querying the database for each user id, is there any way to optimize the foreach loop?
Many thanks