SELECT 
e.objectid as triggerid,
FROM_UNIXTIME(e.clock) as time,
e.`value`,
MIN(FROM_UNIXTIME(e2.clock)) as nextTime
FROM
`events` e
JOIN `events` e2 ON e2.objectid=e.objectid
JOIN functions f ON f.triggerid=e.objectid AND f.triggerid=e2.objectid
JOIN `triggers` t ON t.triggerid=e.objectid AND t.triggerid=e2.objectid
JOIN items i ON i.itemid=f.itemid
JOIN `hosts` h ON h.hostid=i.hostid
JOIN hosts_groups hg ON hg.hostid=h.hostid
WHERE 
e.object=0
AND hg.groupid=13
AND t.description='Availability'
AND e.clock<e2.clock
GROUP BY triggerid, time
ORDER BY triggerid, time DESC

JOIN `events` e2 ON e2.objectid=e.objectid

CREATE FUNCTION NextTime2(`id` int,`curtime` int) RETURN int(11)
BEGIN
DECLARE nextTime INT;
SELECT 
MIN(e.clock)
INTO nextTime
FROM
`events` e
WHERE 
e.objectid=id
AND e.clock>curtime;
RETURN nextTime;
END

SELECT 
e.objectid as triggerid,
FROM_UNIXTIME(e.clock) as Time,
e.`value`,
FROM_UNIXTIME(NextTime2(e.objectid,e.clock)) as nextTime

SET @next_date=NULL, @id=0;
SELECT
t.triggerid,
t.time,
t.`value`,
if(@id=t.triggerid, CAST(@next_date AS CHAR(100) CHARACTER SET utf8), (null) AND (@id:=t.triggerid)) `nextdate`,
@next_date:=t.time
FROM
(
SELECT 
e.objectid as triggerid,
FROM_UNIXTIME(e.clock) as time,
e.`value`
FROM
`events` e
JOIN functions f ON f.triggerid=e.objectid
JOIN `triggers` t ON t.triggerid=e.objectid
JOIN items i ON i.itemid=f.itemid
JOIN `hosts` h ON h.hostid=i.hostid
JOIN hosts_groups hg ON hg.hostid=h.hostid
WHERE 
e.object=0
AND hg.groupid=13
AND t.description='Availability'
ORDER BY e.objectid, e.clock DESC
) as t