How to avoid doing calculation twice

[marathoner]

I'm doing CONVERT_TZ twice in this query and it's horribly inefficient.

Any suggestions for improveing the query will be good.

I know you can set a variable but can you do it in the middle of a query and then reuse it?
Ideally I'd like to eliminate the HAVING too or at least some of it, cuz it's postprocessing

                    

SELECT DISTINCT e.id,name,CONVERT_TZ(startTimestamp,u.sqlTimezone, '" .
                          $this->sqlTimeZone ."') as startTime, timeslots.ord, owner,
                          DATEDIFF(CONVERT_TZ(startTimestamp,u.sqlTimezone, '" .
                          $this->sqlTimeZone ."'), CURDATE()) as ddiff, rsvp as eventcolor,
                          slotbegin,slotend
                    FROM events e,invites i LEFT JOIN rsvps r ON
                       (r.event_id=i.event_id AND r.user = i.user_id ), users u, timeslots
                    WHERE e.id = i.event_id
                    AND i.user_id =  " . $this->id . "
                    AND u.id = e.owner
                     AND timeslots.slottype = 3
                    HAVING TIME(startTime) BETWEEN timeslots.slotbegin AND timeslots.slotend
                    AND startTime BETWEEN CURDATE() AND DATE_ADD(CURDATE(), INTERVAL 4 DAY)
                   ORDER BY startTime