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

Return the names and classes of ships that do not have a captain?
SELECT name, class FROM ship WHERE NOT ship_id IN (SELECT ship_id FROM captain)
SELECT "name", "class" FROM "ship" WHERE NOT "ship_id" IN (SELECT "ship_id" FROM "captain")