[HackerRank SQL] Weather Observation Station 4

문제 link
https://www.hackerrank.com/challenges/weather-observation-station-4/problem

Code link
https://github.com/JamesJung01/Hackerrank_sql/blob/main/01_Easy/Weather_Observation_Stations4.sql

SELECT COUNT(CITY) - COUNT(DISTINCT CITY)
FROM STATION;