具有多个条件和排序的案例陈述

Question

I need to pull from 'world' table and add a CASE WHEN statement to make it so continent name 'Caribbean' changes to 'North America' when country 'name' is LIKE 'B%', but when name is not LIKE 'B%' then continent will='South America'. Also needs to be in ASC order by name.

I know all the commands to do this but can't seem to get them in the right order or syntax. There's the question and screenshot below.

SQL.zoo Problem#13

Answer 1

You just need to break down your problem. Remember CASE will check the cases in order... so if the first case evaluates to TRUE then the following tests are never checked for that row.

You are getting hung up on a multiple condition case statement. Specifically, for the portion you asked about (North America and South America) you need to check two conditions.

1. Is the country in the Caribbean?
2. Does the name Start with a B or not?

So, step through it in order of what they asked.

• Oceania becomes Australasia: when continent = 'Oceania' then 'Australasia'
• Countries in Eurasia and Turkey go to Europe/Asia: when continent = 'Eurasia' or continent = 'Turkey' then 'Europe/Asia'
• Caribbean islands starting with 'B' go to North America, other Caribbean islands go to South America:

when continent = 'Caribbean' and name like 'B%' then 'North America'

when continent = 'Caribbean' and name not like 'B%' then 'South America'

Now put it all together...

select
  name, 
  continent,
  case 
    when continent = 'Oceania' then 'Australasia' 
    when continent = 'Eurasia' or continent = 'Turkey' then 'Europe/Asia'
    when continent = 'Caribbean' and name like 'B%' then 'North America'
    when continent = 'Caribbean' and name not like 'B%' then 'South America'
    else continent 
  end as NewContinent
from
  world
order by 
  name asc