SQL - 예제로 배우는 SQL 3

산하·2022년 4월 8일
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👉🏻 SELECT from WORLD Tutorial


1. Introduction

Q. Observe the result of running this SQL command to show the name, continent and population of all countries.

A.

SELECT name, continent, population FROM world;

2. Large Countries

Q. Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.

A.

SELECT name FROM world
WHERE population > 200000000;

3. Per capita GDP

Q. Show the name for the countries that have a population of at least 200 million. 200 million is 200000000, there are eight zeros.

A.

SELECT name, gdp/population FROM world
WHERE population > 200000000;

4. South America In millions

Q. 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

A.

SELECT name, population/1000000 FROM world
WHERE continent = 'South America';

5. France, Germany, Italy

Q. Show the name and population for France, Germany, Italy

A.

SELECT name, population FROM world
WHERE name IN ('France', 'Germany', 'Italy');

6. United

Q. Show the countries which have a name that includes the word 'United'

A.

SELECT name FROM world
WHERE name LIKE '%United%';

7. Two ways to be big

Q. 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.

A.

SELECT name, population, area FROM world
WHERE area > 3000000 OR population >250000000;

8. One or the other (but not both)

Q. 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 AND population < 250000000 
OR area < 3000000 AND population > 250000000;

9. Rounding

Q. For South America show population in millions and GDP in billions both to 2 decimal places.

A.

SELECT name, ROUND(population/1000000,2), ROUND(gdp/1000000000,2) 
FROM world
WHERE continent = 'South America';

10. Trillion dollar economies

Q. Show per-capita GDP for the trillion dollar countries to the nearest $1000.

A.

SELECT name, ROUND(gdp/population,-3) from world
WHERE gdp > 1000000000000;

11. Name and capital have the same length

Q. 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

A.

SELECT name, capital FROM world
 WHERE LEN(name) = LEN(capital);

12. Matching name and capital

Q. 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.

A.

SELECT name, capital FROM world
WHERE LEFT(name,1) = LEFT(capital,1) AND name != capital

13. All the vowels

Q. 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

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 '% %'

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