Schema: CREATE TABLE chip_model (model_name VARCHAR, chip_model VARCHAR, Accreditation_type VARCHAR); CREATE TABLE phone (model_name VARCHAR, chip_model VARCHAR, Accreditation_type VARCHAR)
Question: Find the names of the chip models that are not used by any phone with full accreditation type.
SQL: SELECT model_name FROM chip_model EXCEPT SELECT chip_model FROM phone WHERE Accreditation_type = 'Full'