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)

How many different captain ranks are there?
SELECT COUNT(DISTINCT rank) FROM captain
SELECT COUNT(DISTINCT "rank") FROM "captain"