How many camera lenses are not used in taking any photos?
select count ( * ) from camera_lens where id not in ( select camera_lens_id from photos )
What is the name of the lenses not used for taking photos?
select name from camera_lens where id not in ( select camera_lens_id from photos )
What is the max aperture for the Olympus M.Zuiko Digital ED 45mm f/1.8?
select max_aperture from camera_lens where name = "Olympus m.zuiko digital ed 45mm f/1.8"