Show me all the phone carriers.
select carrier from phone
The ones with a phones having a price range of 700 to 900?
select carrier from phone where price > 700 and price < 900
How about the ones that have phones both price less than 700 and price more than 900.
select carrier from phone where price < 700 intersect select carrier from phone where price > 900
What about phones with memory less than 32 and memory greater than 64?
select carrier from phone where memory_in_g < 32 intersect select carrier from phone where memory_in_g > 64