select from_unixtime(`your_timestamp`) as lastdt from `sessions`
WHERE from_unixtime(`your_timestamp`) >= NOW() - INTERVAL 15 MINUTE
ORDER BY your_timestamp DESC;
UPDATE report 1 SET status = 'time is larger' WHERE EXISTS
(SELECT ip_src, layer4_sport, timestamp FROM
(SELECT ip_src, layer4_sport, timestamp from report 1) AS tmpb
WHERE report 1.layer4_sport = tmpb.layer4_sport
AND report 1.ip_src = tmpb.ip_src
AND report 1.timestamp > tmpb.timestamp)