Find the average ram mib size of the chip models that are never used by any phone
select avg ( ram_mib ) from chip_model where model_name not in ( select chip_model from phone )
How many chips is that which are never used by any phone?
select count ( * ) from chip_model where model_name not in ( select chip_model from phone )
Give me all their model names and ram mib
select model_name,ram_mib from chip_model where model_name not in ( select chip_model from phone )
How many chips used by phones have a ram mib higher or equal to 64
select count ( * ) from chip_model where model_name in ( select chip_model from phone ) and ram_mib > = 64