Search username

Can anyone please tell me what I need to add to this to pull out the username of the person doing the search? I want to add it (but only viewable to Admins) to keep an eye on who uses the search feature.

$lastsearches=$DB_site->query('SELECT searchid,postids,dateline,querystring FROM search LEFT JOIN user USING (userid) WHERE querystring!="" AND usergroupid NOT IN (5,6,7,9) ORDER BY searchid desc LIMIT 0,15');