sqlzoo答案2-SELECT from WORLD Tutorial

在sqlzoo练习sql：SELECT from WORLD Tutorial - SQLZoo

name	continent	area	population	gdp
Afghanistan	Asia	652230	25500100	20343000000
Albania	Europe	28748	2831741	12960000000
Algeria	Africa	2381741	37100000	188681000000
Andorra	Europe	468	78115	3712000000
Angola	Africa	1246700	20609294	100990000000

1.

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.

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.

Give the name and the per capita GDP for those countries with a population of at least 200 million.

HELP:How to calculate per capita GDP?

per capita GDP is the GDP divided by the population GDP/population

select name,gdp/population 
from world 
where population >=200000000

4.

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.

Show the name and population for France, Germany, Italy

select name,population
from world 
where name in ('France', 'Germany', 'Italy')

6. like

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

select name
from world
where name like '%United%'

7. or

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. xor

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 xor population > 250000000

9. round

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 Americas show population in millions and GDP in billions both to 2 decimal places.

利用round保留两位小数

Millions and billions?

Divide by 1000000 (6 zeros) for millions. Divide by 1000000000 (9 zeros) for billions.

Missing decimals?

For some version of SQL the division of an integer by an integer will be an integer. One way to prevent this is to divide by a floating point number such as 1000000.0.

select name,round(population/1000000,2) ,round(gdp/1000000000,2)
from world
where continent = 'South America' 

10. round this value to the nearest 1000.

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/1000,0)*1000
from world
where gdp >=1000000000000

11. 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

For Microsoft SQL Server the function LENGTH is LEN

SELECT name, capitalFROM worldWHERE LENGTH(name)= LENGTH(capital)

12. left、<>不等于

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) and name <> capital

13.

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'

错误代码：

SELECT nameFROM world
WHERE (name LIKE '%a%'
and name LIKE '%e%'
and name LIKE '%i%'
and name LIKE '%o%'
and name LIKE '%u%' 
or name LIKE 'A%' 
or name LIKE 'E%' 
or name LIKE 'I%' 
or name LIKE 'O%' 
or name LIKE 'U%')AND name NOT LIKE '% %'

SELECT nameFROM world
WHERE (name LIKE '%a%' or name like 'A%'
and name LIKE '%e%' or name LIKE 'E%' 
and name LIKE '%i%' or name LIKE 'I%' 
and name LIKE '%o%' or name LIKE 'O%' 
and name LIKE '%u%' or name LIKE 'U%')AND name NOT LIKE '% %'

如果要考虑首字母的元音字母，那怎么办？

正确代码：

SELECT nameFROM world
WHERE (name LIKE '%a%' or name like 'A%')
and (name LIKE '%e%' or name LIKE 'E%' )
and (name LIKE '%i%' or name LIKE 'I%' )
and (name LIKE '%o%' or name LIKE 'O%' )
and (name LIKE '%u%' or name LIKE 'U%')AND name NOT LIKE '% %'

在sqlzoo上也是正确代码：

SELECT nameFROM 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 '% %'