Tell me all the chip models.
select model_name from chip_model
Tell me all the chip models that are used by phones with full accreditation type.
select t1.model_name from chip_model as t1 join phone as t2 on t1.model_name = t2.chip_model where t2.accreditation_type = 'Full'
How about not used by any phone with full accreditation type?
select model_name from chip_model except select chip_model from phone where accreditation_type = 'Full'