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databases-week1-exercises.sql
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--1. What are the names of countries with population greater than 8 million? | |
SELECT name , Population | |
from city | |
where Population > 8000000 | |
--2. What are the names of countries that have “land” in their names? | |
SELECT Name | |
from city | |
WHERE name like '%land%' | |
--3. What are the names of the cities with population in between 500,000 and 1 million? | |
SELECT name, Population | |
from city | |
where Population > 500000 and Population < 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 = NULL or HeadOfState = ''; | |
--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 LocalName, name | |
from country | |
WHERE Continent = 'Africa' and LocalName = name; | |
--10. What countries have Spanish as official language? Hint: see countrylanguage table | |
SELECT DISTINCT c.Name | |
from countrylanguage cl inner join country c | |
WHERE LANGUAGE = 'Spanish' | |
--11. What countries have official languages spoken between 1% and 10% of the population? | |
SELECT DISTINCT c.Name | |
FROM countrylanguage cl inner join country c | |
WHERE IsOfficial = 'T' and Percentage > 1 and Percentage < 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 c.Name, cl.Percentage FROM countrylanguage cl inner 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 | |
FROM country | |
WHERE GovernmentForm = 'Republic' | |
order by IndepYear ASC 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 AS Country, | |
cl.Language, | |
ROUND((c.Population * cl.Percentage) / 100) 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 AverageEuropeanPopulation | |
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(*) AS NumberOfLanguages | |
FROM | |
countrylanguage | |
WHERE | |
CountryCode = 'BEL' AND | |
IsOfficial = 'T' | |
GROUP BY | |
CountryCode; |
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Question 1: The query is selecting from the city table instead of the country table.
Question 2: The query is selecting from the city table instead of the country table.
Question 7:
HeadOfState = NULL
is incorrect, can you think of another way?Question 9: The query should only select name.
Quetsion 10: The join condition is missing.
Question 11: The percentage should include 1% and 10%.
Question 14: The query returns countries that have a gouvernment form that is exactly "Republic" where we want any form of republic.