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SELECT from WORLD Tutorial
查询表格：
表格说明：
1.Introduction
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
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 or big by population 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.
【知识点】异或
a XOR b，只有当满足条件a或满足条件b，并且不能同时满足ab时，才会被判定为满足条件。
SELECT name, population, area
FROM world
WHERE area > 3000000 XOR population > 250000000
解法2：
SELECT name, population, area FROM world
WHERE (area > 3000000 AND population < 250000000) OR (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.
【知识点】
ROUND()
ROUND(f,p)returns f rounded to p decimal places.
如，ROUND(7253.86, 0)-> 7254
ROUND(7253.86, 1)-> 7253.9
ROUND(7253.86,-3)-> 7000
SELECT name, ROUND(population/1000000,2), ROUND(gdp/1000000000,2)
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
【知识点】
LENGTH()
LENGTH(s)returns the number of characters in string s.
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.
【知识点】
LEFT()
LEFT(s,n)allows you to extract n characters from the start of the string s.
如，LEFT('Hello world', 4)-> 'Hell'
SELECT name, capital
FROM world
WHERE LEFT(name,1) = LEFT(capital,1) AND name <> capital
13.All the vowels
Find the country that has all the vowels and no spaces in its name.
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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