sqlzoo练习答案--SUM and COUNT
2017-08-07 15:35
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World Country Profile: Aggregate functions
This tutorial is about aggregate functions such as COUNT, SUM and AVG. An aggregate function takes many values and delivers just one value. For example the function SUM would aggregate the values 2, 4 and 5 to deliver the single value 11.name | continent | area | population | gdp |
---|---|---|---|---|
Afghanistan | Asia | 652230 | 25500100 | 20343000000 |
Albania | Europe | 28748 | 2831741 | 12960000000 |
Algeria | Africa | 2381741 | 37100000 | 188681000000 |
Andorra | Europe | 468 | 78115 | 3712000000 |
Angola | Africa | 1246700 | 20609294 | 100990000000 |
... |
[sql] view
plain copy
SELECT SUM(population)
FROM world
2、List all the continents - just once each.
[sql] view
plain copy
select DISTINCT(continent) from world
3、Give the total GDP of Africa
[sql] view
plain copy
SELECT SUM(gdp)
FROM world where continent='Africa'
4、How many countries have an area of at least 1000000
[sql] view
plain copy
select count(name) from world where area>1000000
5、What is the total population of ('France','Germany','Spain')
[sql] view
plain copy
SELECT SUM(population)
FROM world where name in('France','Germany','Spain')
6、For each continent show the continent and number of countries.
[sql] view
plain copy
select continent,count(name) from world group by continent
7、For each continent show the continent and number of countries
with populations of at least 10 million.
[sql] view
plain copy
select continent,count(name) from world where population>= 10000000 group by continent
8、List the continents that have a total population of at least 100 million.
[sql] view
plain copy
select continent from world group by continent having sum(population)>=100000000
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