SQL Exercises

Author: ThiagoMowszet

basics.sql

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+-- 1. Introducing the world table of countries
+--The example uses a WHERE clause to show the population of 'France'. Note that strings (pieces of text that are data) should be in 'single quotes'; Modify it to show the population of Germany
+
+SELECT population 
+FROM world
+WHERE name = 'Germany'
+
+
+-- 2. Scandinavia
+-- Checking a list The word IN allows us to check if an item is in a list. The example shows the name and population for the countries 'Brazil', 'Russia', 'India' and 'China'. Show the name and the population for 'Sweden', 'Norway' and 'Denmark'.
+
+SELECT name, population 
+FROM world
+WHERE name IN ('Sweden', 'Norway', 'Denmark');
+
+
+
+-- 3. Just the right size
+-- Which countries are not too small and not too big? BETWEEN allows range checking (range specified is inclusive of boundary values). The example below shows countries with an area of 250,000-300,000 sq. km. Modify it to show the country and the area for countries with an area between 200,000 and 250,000.
+
+SELECT name, area 
+FROM world
+WHERE area BETWEEN 200000 AND 250000

select_from_world.sql

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+-- 1. Introduction
+-- Read the notes about this table. Observe the result of running this SQL command to show the name, continent and population of all countries.
+
+SELECT name, continent, population 
+FROM world
+
+
+
+-- 2. Large Countries
+-- How to use WHERE to filter records. Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.
+
+SELECT name 
+FROM world
+WHERE population >= 200000000
+
+
+
+-- 3. Per capita GDP
+-- Give the name and the per capita GDP for those countries with a population of at least 200 million.
+
+select name, gdp/population
+from world 
+where population > 200000000
+
+
+
+-- 4. South America In millions
+-- Show the name and population in millions for the countries of the continent 'South America'. Divide the population by 1000000 to get population in millions.
+
+select name, population/1000000
+from world
+where continent = 'South America'
+
+
+
+
+-- 5. France, Germany, Italy
+-- Show the name and population for France, Germany, Italy
+
+select name, population 
+from world
+where name in ('France', 'Germany', 'Italy')
+
+
+
+-- 6. United
+-- Show the countries which have a name that includes the word 'United'
+
+select name
+from world
+where name like 'United%'
+
+
+
+-- 7. Two ways to be big
+-- Two ways to be big: A country is big if it has an area of more than 3 million sq km or it has a population of more than 250 million. Show the countries that are big by area or big by population. Show name, population and area.
+
+select name, population, area
+from world
+where area > 3000000 or population > 250000000
+
+
+
+
+-- 8. One or the other (but not both)
+-- Exclusive OR (XOR). Show the countries that are big by area (more than 3 million) or big by population (more than 250 million) but not both. Show name, population and area.
+-- Australia has a big area but a small population, it should be included.
+-- Indonesia has a big population but a small area, it should be included.
+-- China has a big population and big area, it should be excluded.
+-- United Kingdom has a small population and a small area, it should be excluded.
+
+
+select name, population, area
+from world
+where (area > 3000000 or population > 250000000) 
+and not (area > 3000000 and population > 250000000)
+
+
+
+-- 9. rounding
+-- Show the name and population in millions and the GDP in billions for the countries of the continent 'South America'. Use the round function to show the values to two decimal places. For South America show population in millions and GDP in billions both to 2 decimal places.
+
+
+SELECT name, round(population/1000000,2) as Population , round(gdp/1000000000, 2) as GDP
+FROM world
+WHERE continent = 'South America'
+
+
+
+-- 10. Trillion dollar economies
+-- Show the name and per-capita GDP for those countries with a GDP of at least one trillion (1000000000000; that is 12 zeros). round this value to the nearest 1000. Show per-capita GDP for the trillion dollar countries to the nearest $1000.
+
+SELECT name, round(gdp/population, -3)
+FROM world
+WHERE gdp > 1000000000000
+
+
+
+-- 11. Name and capital have the same length
+-- Greece has capital Athens.
+-- Each of the strings 'Greece', and 'Athens' has 6 characters.
+-- Show the name and capital where the name and the capital have the same number of characters.
+-- You can use the LENGTH function to find the number of characters in a string
+
+
+select name, capital
+from world
+where length(name) = length(capital)
+
+
+
+-- 12. Matching name and capital
+-- The capital of Sweden is Stockholm. Both words start with the letter 'S'. Show the name and the capital where the first letters of each match. Don't include countries where the name and the capital are the same word.
+    -- You can use the function LEFT to isolate the first character.
+    -- You can use <> as the not EQUALS operator.
+
+
+SELECT name, capital 
+FROM world
+WHERE left(name, 1) = left(capital, 1) xor name = capital
+
+
+
+-- 13. All the vowels
+-- Equatorial Guinea and Dominican Republic have all of the vowels (a e i o u) in the name. They don't count because they have more than one word in the name. Find the country that has all the vowels and no spaces in its name.
+    -- You can use the phrase name not like '%a%' to exclude characters from your results.
+    -- The query shown misses countries like Bahamas and Belarus because they contain at least one 'a'
+
+
+select name 
+from world
+where name like '%a%' and 
+name  like '%e%' and 
+name  like '%i%' and 
+name  like '%o%' and 
+name  like '%u%' and 
+name not like '% %'