mysql php时间戳查询

Question

I have a online list, I want it to remove the users off list after a certain amount of time they have been inactive.

How would I make the second query work with what im trying to do?

<?php
//On page load with a logged-in user
mysql_query("UPDATE `users` SET `last_activity` = NOW() WHERE `username` = '" . ($_SESSION['username']) . "'");

mysql_query("UPDATE `users` 
             SET `online` = 0 
             WHERE `last_activity` < NOW('+11 minutes') ");
?>  

Right now it, takes away everyone off the list no matter how much time their timestamp is.

Answer 1

You need to use date_sub:

DATE_SUB(NOW(),INTERVAL 11 MINUTE )