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