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

what are the names and classes of the ships that do not have any captain yet?
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")