sql notes: hackerrank asian population

Problem

Given the CITY and COUNTRY tables, query the sum of the populations of all cities where the CONTINENT is ‘Asia’.

Note: CITY.CountryCode and COUNTRY.Code are matching key columns.

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

Analysis

Join two tables on the countrycode.

• join two tables on countrycode ==> FROM CITY AS i JOIN COUNTRY AS o ON i.COUNTRYCODE=o.CODE
• query sum of populations of cities ==> SELECT SUM(i.POPULATION)
• where Continent is ‘Asia’ ==> WHERE o.CONTINENT=‘Asia’

Solution

1

SELECT SUM(i.POPULATION) FROM CITY AS i JOIN COUNTRY AS o ON i.COUNTRYCODE=o.CODE WHERE o.CONTINENT='Asia';

Link

Asian Population
(中文版) SQL 笔记: Hackerrank Asian Population