What is the theme for these cities? | The themes of competitions with host cities having populations larger than 1000 are Carnival M is back!, Codehunters, and MTV Asia Aid | Which cities have populations less than 1000? List their ids.
SELECT DISTINCT T1.CITY_ID FROM city AS T1 JOIN farm_competition AS T2 ON T1.City_ID   =   T2.Host_city_ID WHERE T1.Population  <  1000
cities with populations less than 1000 refers to WHERE Population < 1000; list their ids refers to SELECT DISTINCT CITY_ID;