前两天学习了一下MySQL的基本语法，笔记见：MySQL入门

趁热打铁又开始继续在SQL ZOO 练习，我敲完我笔记的代码，做练习的时候最起码有70%的题是没有问题的，也会有不会的题，在大家的帮助下我做完了90%的练习，剩下的题会继续做的，下面是我觉得有问题或者是需要注意的答案，我做起来觉得很简单的就没有写，当然等我时间充裕会把答案补全，我也在网上查了一些答案，觉得不是很全而且也会有一些错误，希望这些答案可以帮助大家。（ps：这个练习题是英文的，你可以用谷歌浏览器打开，它可以把英文翻译成汉语，当然这个网站也给大家提供了中文翻译，但是繁体字看得我好难受）

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

SELECT name ,population from world where name IN ('France','Germany','Italy')

2.Show the countries which have a name that includes the word ‘United’

SELECT NAME FROM world where name like '%United%'

这道题的意思是查找名字里包含‘United’的，可以用%来完成，%United%表示不管前后是什么，只要包含United就可以，%United表示已United结尾，那你肯定知道United%是什么意思了！

3.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 and population <= 250000000)OR (area<= 3000000 and population > 250000000)

4.Show the name and population in millions and the GDP in billions for the countries of the continent ‘South America’. Use the ROUNDfunction to show the values to two decimal places.

SELECT name,round(population/1000000,2) AS POPULATION,round(GDP/1000000000,2) AS GDP from world where continent ='South America'

5.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

注意：round的用法：

ROUND(7253.86, 0)    ->  7254
ROUND(7253.86, 1)    ->  7253.9
ROUND(7253.86,-3)    ->  7000

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

SELECT yr,subject,winner from nobel where (yr between 1980 and 1989) and subject = 'Literature'

7.Show the name and capital where the name and the capital have the same number of characters.

SELECT name,  capital 
  FROM world where length(name)=length(capital)

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

SELECT YR,SUBJECT,WINNER from nobel where  YR=1980 and subject not in ('Chemistry','Medicine')

9.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 world where continent in
(select continent from world where name in ('Argentina','Australia'))
order by name

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

select name,population from world where (population > 
(select population from world where  name='canada') and  population <(select population from world where name='Poland'))

11.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( population/ (select population from world where name='Germany')*100 ,0),'%') population from world where continent='Europe'

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

SELECT continent, name, area FROM world as x
  WHERE area>= ALL
    (SELECT area FROM world as y
        WHERE y.continent=x.continent
          AND area>0)

any,all的用法：

any 可以与=、>、>=、<、<=、<>结合起来使用，分别表示等于、大于、大于等于、小于、小于等于、不等于其中的任何一个数据。

all可以与=、>、>=、<、<=、<>结合是来使用，分别表示等于、大于、大于等于、小于、小于等于、不等于其中的其中的所有数据。

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

select name from world where gdp >all
(select gdp from world  where continent ='Europe' and GDP>0)

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

SELECT continent, name, area FROM world as x
  WHERE area>=
    (SELECT area FROM world as y
        WHERE y.continent=x.continent
          AND area>0)

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

SELECT continent,name from world a where name <=ALL(select name from world b where a.continent=b.continent)order by name

16.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 x.name, x.continent, x.population
FROM world AS x
WHERE 25000000 > ALL (
  SELECT y.population
  FROM world AS y
  WHERE x.continent = y.continent);

17.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 

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

select continent
from world 
group by continent
HAVING SUM(POPULATION)>=100000000

19.The table eteam gives details of every national team including the coach. You can JOIN goal to eteam using the phrase goal JOIN eteam on teamid=id

Show player, teamid, coach, gtime for all goals scored in the first 10 minutes gtime<=10

 SELECT player, teamid, coach,gtime
  FROM goal 
JOIN eteam 
ON teamid = id
 WHERE gtime<=10

20.Use a different JOIN so that all teachers are listed.

SELECT teacher.name, dept.name
FROM teacher
LEFT JOIN dept
ON teacher.dept = dept.id;

21.Use a different JOIN so that all departments are listed.

SELECT teacher.name, dept.name
FROM teacher
RIGHT JOIN dept
ON teacher.dept = dept.id;

22.Use COALESCE to print the mobile number. Use the number ‘07986 444 2266’ if there is no number given. Show teacher name and mobile number or ‘07986 444 2266’

SELECT name,coalesce(mobile,'07986 444 2266') from teacher

COALESCE的用法：

 COALESCE(x,y,z) = x if x is not NULL
  COALESCE(x,y,z) = y if x is NULL and y is not NULL
  COALESCE(x,y,z) = z if x and y are NULL but z is not NULL
  COALESCE(x,y,z) = NULL if x and y and z are all NULL

23.Use the COALESCE function and a LEFT JOIN to print the teacher name and department name. Use the string ‘None’ where there is no department.

select  teacher.name,coalesce(dept.name, 'None') 
FROM teacher 
LEFT JOIN dept
ON teacher.dept = dept.id

24.Use CASE to show the name of each teacher followed by ‘Sci’ if the teacher is in dept 1 or 2 and ‘Art’ otherwise.

SELECT teacher.name,
case
when teacher.dept in(1,2)
then 'Sci'
ELSE 'Art'
end
from teacher;

25.Use CASE to show the name of each teacher followed by ‘Sci’ if the teacher is in dept 1 or 2, show ‘Art’ if the teacher’s dept is 3 and ‘None’ otherwise.

SELECT teacher.name,
case
when teacher.dept in (1,2)
then 'Sci'
when teacher.dept =3
then 'Art'
else 'None'
end

练习网址：SELECT basics – SQLZOO