ALTER TABLE animals ADD COLUMN compatibility_dogs TEXT NOT NULL DEFAULT 'unknown'
  CHECK (compatibility_dogs IN ('unknown','yes','no'));
ALTER TABLE animals ADD COLUMN compatibility_cats TEXT NOT NULL DEFAULT 'unknown'
  CHECK (compatibility_cats IN ('unknown','yes','no'));
ALTER TABLE animals ADD COLUMN compatibility_children TEXT NOT NULL DEFAULT 'unknown'
  CHECK (compatibility_children IN ('unknown','yes','no'));
ALTER TABLE animals ADD COLUMN house_trained TEXT NOT NULL DEFAULT 'unknown'
  CHECK (house_trained IN ('unknown','yes','no'));