databases-week1-exercises.sql

-- 1. What are the names of countries with population greater than 8 million?
SELECT Name 
FROM country
WHERE Population > 8000000;

-- 2. What are the names of countries that have “land” in their names?
SELECT name FROM country WHERE name LIKE '%land%';

-- 3. What are the names of the cities with population in between 500,000 and 1 million?
SELECT name from city where Population BETWEEN 500000 AND 1000000;

-- 4. What's the name of all the countries on the continent ‘Europe’?
SELECT name FROM country where Continent = 'Europe'

-- 5. What are the names of all the cities in the Netherlands?
SELECT name FROM city WHERE CountryCode = 'NLD'

-- 6. What is the population of Rotterdam?
SELECT Population FROM city where name = 'Rotterdam'

-- 7. Which countries don't have a head of state? Hint: looks for NULL and '' values
select Name from country WHERE HeadOfState = '' or HeadOfState  IS NULL

-- 8. What's the top 10 least populated cities? Return the name and population
SELECT name, Population FROM city ORDER BY Population LIMIT 10

-- 9. What countries in Africa have the local name the same as their common name?
SELECT name FROM country where Continent = 'Africa' AND Name = LocalName

-- 10. What countries have Spanish as official language? Hint: see countrylanguage table
SELECT country.name, countrylanguage.language
FROM
country
JOIN
countrylanguage
ON country.Code  = countrylanguage.countrycode
WHERE countrylanguage.language = 'Spanish' AND countrylanguage.IsOfficial = 'T'

-- 11. What countries have official languages spoken between 1% and 10% of the population?
SELECT country.name, countrylanguage.language, countrylanguage.Percentage
FROM
country
JOIN
countrylanguage
ON country.Code  = countrylanguage.countrycode
WHERE countrylanguage.IsOfficial = 'T' and countrylanguage.Percentage BETWEEN 1 and 10

-- 12. What languages are spoken by over 90% of the population of a country? Return just the language names, but don't repeat entries
SELECT DISTINCT language 
FROM countrylanguage 
WHERE Percentage > 90;

-- 13. In which countries is 'Creole English' used? Order by descending percentage of speakers
SELECT country.Name
FROM
country
JOIN
countrylanguage
ON country.Code  = countrylanguage.countrycode
WHERE countrylanguage.language = 'Creole English'
ORDER BY countrylanguage.Percentage DESC 

-- 14. What are the 5 oldest countries (by independence date) with some form of republic government? Tip: there are multiple types of republic
SELECT country.Name, country.indepyear, country.GovernmentForm
FROM
country
WHERE country.GovernmentForm LIKE '%Republic%'
ORDER BY country.IndepYear LIMIT 5

-- 15. For each country, how many people speak each language? Important: we want absolute values, not a percentage. Return the name of the country, the name of the language, and number of speakers of that language - Hint: you need both the country and countrylanguage tables - Hint: you can do calculations between columns, for example (SELECT a - b from table;)
SELECT country.Name, countrylanguage.language, country.Population * (countrylanguage.Percentage/100) AS 'Number of Speakers' 
FROM
country
JOIN
countrylanguage
ON country.Code  = countrylanguage.countrycode

-- BONUS
-- 1. What is the total population of the world?
SELECT SUM(Population) as "World's Total Population" FROM country

-- 2. What is the average population of countries in Europe?
SELECT AVG(Population) as 'Average Population in Europe' FROM country
WHERE Continent = 'Europe'

-- 3. How many *official* languages are spoken in Belgium (`BEL`)? Return the country code, and the number of languages as "Number of Languages"
SELECT CountryCode, COUNT(language) as 'Number of Languages' FROM countrylanguage
WHERE CountryCode = 'BEL' AND IsOfficial = 'T'

Hi Sebastien, thank you for the suggestions, I have corrected the queries.