Number of entries in DB PHP - php

Question

I am creating a function to show how many users are online now. This is based on who has opened a page within the last 5 min. Each page load is saved to my DB, below:
At the moment I have the following code
$query = mysql_query("SELECT user_id, timestamp FROM user_actions WHERE timestamp > date_sub(now(), interval 5 minute)");
$onlineUsers = mysql_num_rows($query);
This is simply totalling the number of rows, how can I do this so it only counts a user_id once? (so in the above database snippet it should be 2 not 5)

Answer 1

use DISTINCT keyword
$query = mysql_query("SELECT DISTINCT(user_id), timestamp FROM user_actions WHERE timestamp > date_sub(now(), interval 5 minute)");
$onlineUsers = mysql_num_rows($query);

Answer 2

Since mysql_* is deprecated (php 5 onward) and removed in (php 7). So a mysqli_* example is here:-
<?php
error_reporting(E_ALL);
ini_set('display_errors',1);
$conn = mysqli_connect('localhost','username','password','db name');//change credentials here
$online_users = array();
if($conn){
$query = mysqli_query($conn,"SELECT DISTINCT(user_id), timestamp,page FROM user_actions WHERE timestamp > date_sub(now(), interval 5 minute)");
if($query){
while($row = mysqli_fetch_assoc($query)){
$online_users[] = $row;
}
}else{
echo "query error:-".mysqli_error($conn);
}
}else{
echo "db connection error:-".mysqli_connect_error();
}
?>
<table>
<tr>
<thead>
<th>User Id</th>
<th>timestamp></th>
<th>Page Visited</th>
</thead>
</tr>
<tbody>
<?php foreach($online_users as $online_user){?<
<tr>
<td><?php echo $online_user['user_id'];?></td>
<td><?php echo $online_user['timestamp'];?></td>
<td><?php echo $online_user['page'];?></td>
</tr>
<?php }?>
</tbody>
</table>
Note:- If you want to show online user name also then you have to do JOIN query.
change table code accordingly.
It's a sample code. modify it accordingly.

Answer 3

You may use group by, e.g
SELECT user_id, timestamp FROM user_actions WHERE timestamp > date_sub(now(), interval 5 minute) group by user_id;