Code stops working after I add a new colunm to Table - php

Question

The code below a member and guest counter . The code runs perfectly however when I add a simple column (online) to the table active_members the entire code stops working (apart from the active_guests as this a separate table)
I have looked tirelessly trying to catch anything that may be causing this I have included the table screenshot below . I would to had add new column (online)that is a varchar to the table members_online and then query in the if SESSION below for that new column .
Why does the code stop working , Can somebody possible see the cause or solution?
As soon as i remove the online column is code runs perfect again .
$sqlt2 query below is the line I want to index the new online column .
include('..\db.php');
$con = mysqli_connect($dbsrvname, $dbusername, $dbpassword, $dbname);
//declare variables
$guest_timeout = time() -1 * 60;
$member_timeout = time() -1 * 60;
$guest_ip = $_SERVER['REMOTE_ADDR'];
$time = time();
// if the session is set PUTS THE USER IN MEMBERS TABLE
if(isset($_SESSION['CurrentUser'])){
//if user is logged in
$sqlt = mysqli_query($con,"DELETE FROM active_guests WHERE guest_ip='".$guest_ip."'");
**//I WANT TO ADD TO THE ONLINE COLUMN AND REPLACE A SIMPLE STRING INTO ONLINE**
$sqlt2 = mysqli_query($con,"REPLACE INTO active_members VALUES ('".$_SESSION['CurrentUser']."','".$time."')");
$name = $_SESSION['CurrentUser'] ;
}else{
//if user not in a session PUTS THE USER IN GUESTS TABLE
$sqlt3 = mysqli_query($con,"REPLACE INTO active_guests (guest_ip,time_visited)VALUES ('".$guest_ip."','".$time."')");
}
//execute querys
$sqlt4 = mysqli_query($con,"DELETE FROM active_guest WHERE time_visited < ".$guest_timeout);
$sqlt5 = mysqli_query($con,"DELETE FROM active_members WHERE time_visited < ".$member_timeout);
$sqlt6 = mysqli_query($con,"SELECT guest_ip FROM active_guests");
$sqlt7 = mysqli_query($con,"SELECT username FROM active_members");
$online_guests = mysqli_num_rows($sqlt6);
if(isset($_SESSION['CurrentUser'])){
$sqlt7 = mysqli_query($con,"SELECT username FROM active_members");
if($sqlt7->num_rows){
while($row = $sqlt7->fetch_object())
{
echo '<pre>',$row->username,'</pre>' ;
}
//$result->free();
}
}else{
echo "Login to see members-online list";
}
$online_members = mysqli_num_rows($sqlt7);
?>
// display results
<div class="container">
<p>_________________________</p>
<p>online Guests : <?php echo $online_guests ; ?></p>
<p>online Members : <?php echo $online_members ; ?></p>
</div>

Answer 1

Set column "online"s "Default/Expression" to null, hopefully it'll will work!