CREATE TABLE mountain (id NUMBER, name CLOB, height NUMBER, prominence NUMBER, range CLOB, country CLOB)
CREATE TABLE camera_lens (id NUMBER, brand CLOB, name CLOB, focal_length_mm NUMBER, max_aperture NUMBER)
CREATE TABLE photos (id NUMBER, camera_lens_id NUMBER, mountain_id NUMBER, color CLOB, name CLOB)

How many camera lenses are not used in taking any photos?
SELECT COUNT(*) FROM camera_lens WHERE NOT id IN (SELECT camera_lens_id FROM photos)
SELECT COUNT(*) FROM "camera_lens" WHERE NOT "id" IN (SELECT "camera_lens_id" FROM "photos")