CREATE TABLE ship (ship_id NUMBER, name CLOB, type CLOB, built_year NUMBER, class CLOB, flag CLOB)
CREATE TABLE captain (captain_id NUMBER, name CLOB, ship_id NUMBER, age CLOB, class CLOB, rank CLOB)

Return the rank for which there are the fewest captains.
SELECT rank FROM captain GROUP BY rank ORDER BY COUNT(*) DESC LIMIT 1
SELECT "rank" FROM "captain" GROUP BY "rank" ORDER BY COUNT(*) DESC FETCH FIRST 1 ROWS ONLY