title: select from mysql table between datetime x min ago and datetime x min ago
body: <p>I think I summed nicely it up in the title. I want to select online users from a specific time to another specific time. My table look like this:</p>
  
  <pre><code>CREATE TABLE online (
  
      id bigint(20) NOT NULL auto_increment,
      `username` varchar (16) NOT NULL, 
      `ip` varchar(39) NOT NULL default '',   
      `time` datetime NOT NULL default '0000-00-00 00:00:00' ,
  
        PRIMARY KEY  (id)
  );
  </code></pre>
  
  <p>I want a query that return the <code>username</code>'s that have been online the <code>last 15 minutes</code>. </p>
  
  <p>And a query for the users that have been online the <code>last 60 minutes, but not the last 15 minutes</code>. So the query's don't return the same values. This I don't know how to do. </p>