CREATE TABLE county_public_safety (county_ID VARCHAR, population INT)
CREATE TABLE city (county_ID VARCHAR, population INT)

Show the number of cities in counties that have a population more than 20000.
SELECT COUNT(*) FROM city WHERE county_ID IN (SELECT county_ID FROM county_public_safety WHERE population > 20000)
SELECT COUNT(*) FROM "city" WHERE "county_ID" IN (SELECT "county_ID" FROM "county_public_safety" WHERE "population" > 20000)