1. Show the name - but substitute Australasia for Oceania - for countries beginning with N.

显示以N开头的国家并且用Australasia代替Oceania

答案：SELECT name, CASE WHEN continent='Oceania' THEN 'Australasia ELSE continent END  FROM world WHERE name LIKE 'N%'；

2. Show the name and the continent - but substitute Eurasia for Europe and Asia; substitute America- for each country in North America or South America or Caribbean. Show countries beginning with A or B

答案：SELECT name,CASE WHEN continent IN ('Europe','Asia') THEN 'Eurasia' 

WHEN continent IN('North America','South America','Caribbean') THEN 'America'  

ELSE continent 

END

FROM world 

WHERE name LIKE 'A%' OR name LIKE 'B%'

用到的关键语法，替换：CASE WHEN ... THEN ... WHEN... THEN... ELSE... END 

3. Put the continents right...

Oceania becomes Australasia

Countries in Eurasia and Turkey go to Europe/Asia

Caribbean islands starting with 'B' go to North America, other Caribbean islands go to South America

Show the name, the original continent and the new continent of all countries.

答案：

SELECT name,continent,

CASE

WHEN continent = 'Oceania' THEN 'Australasia'

WHEN continent IN ('Eurasia','Turkey') THEN 'Europe/Asia'

WHEN continent = 'Caribbean'THEN

CASE

WHEN name LIKE 'B%' THEN 'North America'

ELSE 'South America'

END

ELSE continent

END

FROM world

ORDER BY name