SQLite 3.27

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TABLE animals (`animal` VARCHAR(12), `pof` VARCHAR(6));
INSERT INTO animals (`animal`, `pof`) VALUES
  ('fish', 'pet'),
  ('fish', 'food'),
  ('pig', 'food'),
  ('cat', 'pet'),
  ('dog', 'pet'),
  ('horse', 'pet'),
  ('mouse', 'pet'),
  ('duck', 'pet'),
  ('duck', 'food'),
  ('cow', 'food'),
  ('rabbit', 'pet'),
  ('rabbit', 'food'),
  ('gerbil', 'pet'),
  ('worm', null),
  ('chicken', 'food');
select *
from animals
where pof = 'pet'
and animal not in (select animal from animals where pof = 'food')


animal
pof


cat
pet

dog
pet

horse
pet

mouse
pet

gerbil
pet


select animal from animals where pof = 'pet'
except
select animal from animals where pof = 'food'


animal


cat

dog

gerbil

horse

mouse