DELETE FROM `80dage_garmin_track` t1
WHERE EXISTS (SELECT 1 from `80dage_garmin_track` t2
WHERE t1.Length = t2.Length
AND t1.Time = t2.Time
AND t1.idgarmin_track > t2.idgarmin_track)
DELETE FROM `80dage_garmin_track` t1
WHERE EXISTS (SELECT 1 from `80dage_garmin_track` t2
WHERE t1.Length = t2.Length
AND t1.Time = t2.Time
AND t1.idgarmin_track > t2.idgarmin_track)