SQLZOO 練習筆記

09-17

SQLZOO 練習筆記

一、SELECT basics

1.Modify it to show the population of Germany

select population from world where name=Germany

2.Show the name and the population for Sweden, Norway and Denmark.

select name,population from world where name in( Sweden, Norway,Denmark)

3.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

二、SELECT from WORLD Tutorial

1.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.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.

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

4.how 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. 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: 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.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.

select name,population,area from world where area > 3000000 xor population >250000000

9. 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),round(gdp/1000000000,2) from world where continent=South America

10.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.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. 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. Dont 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 dont count because they have more than one word in the name.

14.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% %

三、SELECT from Nobel Tutorial

Change the query shown so that it displays Nobel prizes for 1950.

select yr, subject, winner from nobel where yr=1950

Show who won the 1962 prize for Literature.

select winner from nobel where yr=1962 and subject=Literature

Show the year and subject that won Albert Einstein his prize.

select yr,subject from nobel where winner=Albert Einstein

Give the name of the Peace winners since the year 2000, including 2000.

select winner from nobel where subject=Peace and yr>=2000

5.Show all details (yr, subject, winner) of the Literature prize winners for 1980 to 1989 inclusive.

select yr,subject,winnerfrom nobel where subject=Literature and yr between 1980 and 1989

6.Show all details of the presidential winners:

Theodore Roosevelt
Woodrow Wilson
Jimmy Carter
Barack Obama

select * from nobel where winner in(Theodore Roosevelt,Woodrow Wilson,Jimmy Carter,Barack Obama)

7. Show the winners with first name John

select winner from nobel where winner likeJohn%

8. Show the year, subject, and name of Physics winners for 1980 together with the Chemistry winners for 1984.

select yr,subject,winner from nobel where (subject=Physics and yr=1980) or (subject=Chemistry and yr=1984)

9. Show the year, subject, and name of winners for 1980 excluding Chemistry and Medicine

select yr,subject,winner from nobel where subject not in(Chemistry, Medicine) and yr=1980

10. Show year, subject, and name of people who won a Medicine prize in an early year (before 1910, not including 1910) together with winners of a Literature prize in a later year (after 2004, including 2004)

select yr,subject,winner from nobel where (subject=Medicine and yr < 1910) or (subject=Literature and yr >= 2004)

11. Find all details of the prize won by PETER GRüNBERG

select * from nobel where winner=PETER GRüNBERG

12. Find all details of the prize won by EUGENE ONEILL

select * from nobel where winner likeEUGENE ONEILL #這裡引號使用注意

13. List the winners, year and subject where the winner starts with Sir. Show the the most recent first, then by name order.

select winner,yr,subjectfrom nobel where winner likeSir% order by yr desc, winner

14.The expression subject IN (Chemistry,Physics) can be used as a value - it will be 0 or 1.

Show the 1984 winners and subject ordered by subject and winner name; but list Chemistry and Physics last.

select winner, subjectfrom nobelwhere yr=1984order by subject in (Physics,Chemistry),subject,winner

四、SELECT within SELECT Tutorial

This tutorial looks at how we can use SELECT statements within SELECT statements to perform more complex queries.

1.List each country name where the population is larger than that of Russia.

select name from world where population>(select population from world where name=Russia)

2. Show the countries in Europe with a per capita GDP greater than United Kingdom.

select name from worldwhere gdp/population > (select gdp/population from world where name=United Kingdom ) and continent=Europe

3.List the name and continent of countries in the continents containing either Argentina or Australia. Order by name of the country.

select name,continent from worldwhere continent in (select continent from world where name=Argentina or name=Australia)order by name

4.Which country has a population that is more than Canada but less than Poland? Show the name and the population.

select name,population from worldwhere population> (select population from world where name=Canada )and population <(select population from world where name=Poland)

5. Germany (population 80 million) has the largest population of the countries in Europe. Austria (population 8.5 million) has 11% of the population of Germany.

Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.

select name,concat(round(100*population/(select population from world where name=Germany)),%)from worldwhere continent=Europe

6.Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)

select namefrom worldwhere gdp > all(select gdp from world where continent=Europe and gdp>0)

7.Find the largest country (by area) in each continent, show the continent, the name and the area:

select continent,name,area from world xwhere x.area >= all(select y.area from world y where y.continent=x.continent and area>0)

8. List each continent and the name of the country that comes first alphabetically.

select continent,name from world xwhere x.name=(select y.name from world y where x.continent=y.continent order by name limit 1)

9. Find the continents where all countries have a population <= 25000000. Then find the names of the countries associated with these continents. Show name, continent and population.

select name,continent,population from world x where 25000000 >=all(select y.population from world y where x.continent=y.continent and population>0)

10. Some countries have populations more than three times that of any of their neighbours (in the same continent). Give the countries and continents.

select name,continent from world xwhere x.population >=all(select y.population*3 from world y where y.continent=x.continent and population >0 and x.name!=y.name )

五、SUM and COUNT

World Country Profile: Aggregate functions

This tutorial is about aggregate functions such as COUNT, SUM and AVG. An aggregate function takes many values and delivers just one value. For example the function SUM would aggregate the values 2, 4 and 5 to deliver the single value 11.

1. Show the total population of the world.

select sum(population) from world

2. List all the continents - just once each.

select distinct continent from world

3. Give the total GDP of Africa

select sum(gdp) from world where continent=africa

4. How many countries have an area of at least 1000000

select count(name) from world where area >= 1000000

5. What is the total population of (Estonia, Latvia, Lithuania)

select sum(population) from world where name in(Estonia, Latvia, Lithuania)

6. For each continent show the continent and number of countries.

select continent,count(name) from world group by continent

7. For each continent show the continent and number of countries with populations of at least 10 million.

select continent,count(name) from world where population >=10000000 group by continent

8. List the continents that have a total population of at least 100 million.

select continent from world group by continenthaving sum(population)>100000000