CREATE TABLE Aircraft (name VARCHAR2, aid VARCHAR2)
CREATE TABLE Certificate (aid VARCHAR2)

Show the name 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(*) DESC LIMIT 1
SELECT "T2"."name" FROM "Certificate" "T1" JOIN "Aircraft" "T2" ON "T1"."aid" = "T2"."aid" GROUP BY "T1"."aid" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY