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-- 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, HeadOfState | |
from country | |
WHERE HeadOfState is NULL or ''; | |
-- 8. What's the top 10 least populated cities? Return the name and population | |
SELECT name, population | |
from city | |
order by Population ASC LIMIT 10; | |
-- 9. What countries in Africa have the local name the same as their common name? | |
SELECT Name, LocalName | |
FROM country | |
WHERE Continent = 'Africa' AND Name = LocalName; | |
-- 10. What countries have Spanish as official language? Hint: see countrylanguage table | |
SELECT name | |
FROM country | |
JOIN countrylanguage on country.Code = countrylanguage.CountryCode | |
WHERE LANGUAGE='spanish' and IsOfficial ='t' ; | |
-- 11. What countries have official languages spoken between 1% and 10% of the population? | |
SELECT country.name | |
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 cl.Language | |
FROM countrylanguage cl | |
WHERE cl.Percentage > 90; | |
-- 13. In which countries is 'Creole English' used? Order by descending percentage of speakers | |
SELECT cl.CountryCode, c.Name, cl.Percentage | |
FROM countrylanguage cl | |
JOIN country c ON cl.CountryCode = c.Code | |
WHERE cl.Language = 'Creole English' | |
ORDER BY cl.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 name, IndepYear, GovernmentForm | |
FROM country c | |
WHERE GovernmentForm LIKE '%republic%' | |
ORDER BY 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 c.Name, cl.Language, ROUND((cl.Percentage / 100) * c.Population) AS NumberOfSpeakers | |
FROM country c | |
JOIN countrylanguage cl ON c.Code = cl.CountryCode; | |
-- BONUS | |
-- 1. What is the total population of the world? | |
SELECT SUM(Population) AS TotalWorldPopulation | |
FROM country; | |
-- 2. What is the average population of countries in Europe? | |
SELECT AVG(Population) AS AveragePopulation | |
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' | |
GROUP BY countrycode; | |
-- MORE | |
-- 1. Retrieve the names of all the cities along with their respective country names, make sure the column names are easy to understand. | |
SELECT city.name AS city,country.Name AS country | |
FROM city | |
JOIN country ON city.CountryCode =country.Code ; | |
-- 2. Find the average life expectancy of countries in the continent 'Europe'. | |
SELECT AVG(LifeExpectancy) | |
FROM country | |
WHERE Continent = "Europe"; | |
-- 3. Get the names and populations of cities in the district 'California'. | |
SELECT name, Population | |
FROM city | |
WHERE District = 'California'; | |
-- 4. Retrieve the capital city of each country along with the country name. | |
SELECT country.name AS country_name, city.name AS capital_city | |
FROM country | |
JOIN city ON country.capital = city.id; | |
-- 5. Find the largest city by population in each country. | |
-- Tip: It is possible to use nested queries, for example, if you wanted to get all the countries which population | |
-- is greater than Spain's you would do: | |
-- SELECT Name FROM country WHERE Population > (SELECT Population FROM country WHERE Name = 'Spain') | |
SELECT country.name AS country_name, city.name AS city_name, city.population | |
FROM city | |
JOIN country ON city.CountryCode = country.Code | |
WHERE city.population = (SELECT MAX(population) FROM city WHERE CountryCode = city.CountryCode); | |
-- 6. List the names of all cities with a population of over 1 million in the continent of 'Asia'. | |
SELECT city.Name | |
FROM city | |
JOIN country | |
WHERE city.CountryCode =country.Code AND country.Continent ='Asia' and city.Population >1000000; | |
-- 7. Get the names and continents of countries that do not have an official language recorded in the database. | |
SELECT country.Name ,country.Continent | |
FROM country | |
Left JOIN countrylanguage | |
ON country.code = countrylanguage.countrycode AND countrylanguage.isofficial = 'T' | |
WHERE countrylanguage.countrycode IS NULL AND countrylanguage.Language IS NULL; | |
-- 8. List the countries in the 'Oceania' continent with an average life expectancy over 70. | |
SELECT name | |
FROM country | |
WHERE Continent = "oceania" ANd LifeExpectancy > 70; | |
-- 9. Find the total number of languages spoken in the continent 'Africa'. | |
SELECT COUNT(countrylanguage.Language) AS "Total number of Languages in Africa" | |
From country | |
LEFT JOIN countrylanguage | |
ON country.code = countrylanguage.countrycode | |
WHERE country.Continent ='Africa' ; | |
-- 10. Retrieve the names and populations of cities located in countries with a surface area greater than 1 million square kilometers. | |
SELECT city.name AS city_name, city.population | |
FROM city | |
JOIN country ON city.CountryCode = country.code | |
WHERE country.surfaceArea > 1000000; | |
-- 11. Retrieve the names and populations of capital cities with populations over 500,000. | |
SELECT city.name, country.population | |
FROM city | |
JOIN country ON country.code = city.countrycode | |
WHERE country.population > 500000; | |
-- 12. List the names and continents of countries where English is an official language. | |
SELECT country.Name ,country.Continent | |
FROM country | |
JOIN countrylanguage | |
ON country.code = countrylanguage.countrycode AND countrylanguage.isofficial = 'T' | |
WHERE countrylanguage.`Language` ="English"; | |
-- 13. Find the name of the country with the highest life expectancy. | |
SELECT name | |
From country | |
ORDER by LifeExpectancy DESC limit 1; | |
-- 14. Get the names of countries in the 'South America' continent with cities having a population over 1 million. | |
SELECT country.Name | |
FROM country | |
JOIN city | |
ON country.code = city.CountryCode | |
WHERE country.Continent="South America" AND city.Population >1000000 | |
-- 15. Find the name and population of the smallest city (by population) in the country 'India'. | |
SELECT city.Name ,city.Population | |
FROM country | |
JOIN city | |
ON country.code = city.CountryCode | |
WHERE country.Name ="India" ORDER BY city.Population ASC LIMIT 1 ; | |
-- 16. Retrieve the country name and its corresponding capital city's name where the capital's population is more than 1 million. | |
SELECT country.Name ,city.Name | |
FROM country | |
JOIN city | |
ON country.code = city.CountryCode | |
WHERE city.Population >1000000 ; | |
-- 17. List the names of countries that have no cities in the database. | |
SELECT country.Name | |
FROM country | |
Left JOIN city | |
ON country.code =city.countrycode | |
WHERE city.Name IS NULL; | |
-- Um LEFT JOIN retorna todos os registros da tabela à esquerda (primeira tabela mencionada após o FROM), | |
mesmo que não haja correspondências na tabela à direita (segunda tabela mencionada após o LEFT JOIN). | |
-- 18. Get the name and population of the largest city in the continent 'South America'. | |
SELECT city.Name,city.Population | |
FROM city | |
JOIN country | |
ON city.countrycode= country.code | |
WHERE country.Continent ="South America" ORDER by city.Population DESC limit 1 ; | |
-- 19. List the names and populations of all cities in countries where the official language is 'Spanish'. | |
SELECT city.Name,city.Population | |
FROM city | |
JOIN country ON city.countrycode= country.code | |
JOIN countrylanguage ON city.countrycode= countrylanguage.CountryCode | |
WHERE countrylanguage.`Language` ="Spanish" AND countrylanguage.IsOfficial ="T"; | |
-- 20. Get the name of the country and the population of the city with the highest population in that country. | |
SELECT country.Name, city.Population | |
FROM country | |
JOIN city | |
ON country.code= city.countrycode | |
ORDER by city.Population DESC limit 1 ; |
Hello Sebastian, thank you very much for your help. I will fix.
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Question 8: The query orders by descending population, which returns the most populated cities instead of the least populated ones.
Question 13: The query should join with the
country
table to get the country names.Question 7 (More): The query should check countrylanguage.Language IS NULL to identify countries without any official language records.