WHAT ARE THE NAMES OF AIRCRAFT WHICH FEWEST PEOPLE HAVE ITS CERTIFICATE
SELECT T2.name FROM Certificate AS T1 JOIN Aircraft AS T2 ON T2.aid   =   T1.aid GROUP BY T1.aid ORDER BY count ( * )  ASC LIMIT 1
aircraft with the fewest people having its certificate refers to MIN(COUNT(certificates)); names of aircraft refers to Aircraft.name; joining tables Certificate and Aircraft on matching aircraft IDs (aid);