Hello there!  Can you tell me what is the sum total of the populations of the three districts with the largest area?
select sum ( city_population ) from district order by city_area desc limit 3
Excellent!  Can you tell me the district name associated with the largest population?
select district_name from district where city_population = ( select max ( city_population ) from district )
Wonderful!  Can you show me the city's population total and the city's area?
select city_population, city_area from district where city_population = ( select max ( city_population ) from district )