sql notes: hackerrank average population of each continent

Problem

Given the CITY and COUNTRY tables, query the names of all the continents (COUNTRY.Continent) and their respective average city populations (CITY.Population) rounded down to the nearest integer.

Note: CITY.CountryCode and COUNTRY.Code are matching key columns. Do not include continents without cities in your output.

Input Format
The CITY and COUNTRY tables are described as follows:

Analysis

• join two tables ==> FROM CITY AS i JOIN COUNTRY AS o ON i.COUNTRYCODE=o.CODE
• query names of continents ==> SELECT o.CONTINENT
• respective city average population ==> AVG(i.POPULATION) … GROUP BY o.CONTINENT
• round down to nearest integer ==> FLOOR(AVG(i.POPULATION)) … GROUP BY o.CONTINENT

Solution

1

SELECT o.CONTINENT, FLOOR(AVG(i.POPULATION)) FROM CITY AS i JOIN COUNTRY AS o ON i.COUNTRYCODE=o.CODE GROUP BY o.CONTINENT;

Link

Average Population of Each Continent
(中文版) SQL 笔记: Hackerrank Average Population of Each Continent