[HackerRank|MySQL] Average Population / Japan Population / Population Density Difference

Average Population

Problem

Query the average population for all cities in CITY, rounded down to the nearest integer.

Solution

SELECT FLOOR(AVG(POPULATION))
FROM CITY

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Japan Population

Problem

Query the sum of the populations for all Japanese cities in CITY. The COUNTRYCODE for Japan is JPN.

Solution

SELECT SUM(POPULATION)
FROM CITY
WHERE COUNTRYCODE = 'JPN'

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Population Density Difference

Problem

Query the difference between the maximum and minimum populations in CITY.

Solution

SELECT MAX(POPULATION) - MIN(POPULATION)
FROM CITY