[HackerRank] Revising Aggregations, Populations

https://www.hackerrank.com/challenges/revising-aggregations-sum/problem?isFullScreen=true&h_r=next-challenge&h_v=zen 

Revising Aggregations - The Sum Function | HackerRank

 

쿼리가 짧고 간단한게 연속으로 나와서, 하나의 포스트에 정리하겠다. 

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Revising Aggregations - The Sum Function

Query the total population of all cities in CITY where District is California.

Input Format

The CITY table is described as follows: 

SELECT SUM(POPULATION)
FROM CITY 
WHERE DISTRICT ='California'

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Revising Aggregations - AVERAGES

Query the average population of all cities in CITY where District is California.

SELECT AVG(POPULATION)
FROM CITY
WHERE DISTRICT ='California'

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Revising Aggregations - Average Population

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

# 정수일때는 round (원하는 숫자, 0)
# 수수점이 늘어갈때마다 1씩 뒤에 추가

SELECT ROUND(AVG(POPULATION),0)
FROM CITY

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Revising Aggregations - Japan Population

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

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

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Revising Aggregations - Population Density Difference

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

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

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간단하게 계산하는 함수들 쓰는걸 한번 집고 넘어가는 느낌이다.