FROM tablename AS t1, tablename AS t2
WHERE t1.lnktxt = t2.lnktxt
AND t1.cattxt = t2.cattxt
AND t1.datetxt < t2.datetxt
ALSO: If you happen to have 3 (or more!) records with the same lnktxt and cattxt values, that will delete *all* of them except the one with the latest datetxt field.