使用PHP计算在线用户数量

Question

I'm trying to count how many users are online on my site within 10 minutes and display it, but I'm facing some problems with my code.

//Count online users
//Data on DB: 2016-06-08 03:15:21

    $onlinesql = $odb -> prepare("SELECT `users`.`lastactivity`  count(*) FROM `users` WHERE `lastactivity` >= DATE_SUB(NOW(), INTERVAL 10 MINUTE");
    $onlinesql -> execute(array(":id" => `lastactivity`));
    $rowonline = $onlinesql -> fetch(); 

    echo $rowonline;

It's not returning the number of online users, how can I get it working?

Answer 1

SELECT count(*) FROM `users` WHERE `lastactivity` >= DATE_SUB(NOW(), INTERVAL 10 MINUTE)

无需使用count（ id ）或count（ lastactivity ），只需使用count（*），因为这是最快的方法

Answer 2

You may want to revisit your SQL. Here's an Example:

    <?php    
        $sql        = "SELECT COUNT(U.*) FROM `users` U WHERE u.lastactivity >= DATE_SUB( NOW(), INTERVAL 10 MINUTE)";
        $onlineSQL  = $odb ->prepare($sql);
        $onlineSQL  -> execute();
        $numOnline  = $onlineSQL->fetch();

        var_dump($numOnline);

Answer 3

You can use ajax. create an enum field in users table lets call it (status) '0'=> offline and '1'=> online and make two setInterval functions one to update user status each 2 minutes for example with ajax and another one to get count of users with status '1' from database with ajax too.