为什么ALL关键字在此查询中不起作用？

Question

I have following SQL query:

SELECT 
    name
FROM 
    world
WHERE
    gdp > ALL (SELECT gdp FROM world WHERE continent = 'Europe')

I'm running this query at sqlzoo to find countries that have a GDP greater than every country in Europe.

The expected result is United States, China. The ALL keyword is supposed to make > work over a list. It doesn't in this case. Why?

Answer 1

It does work at least with MySQL. But you also have to exclude the countries in Europe that have null GDPs:

SELECT 
    name
FROM 
    world
WHERE
    gdp > ALL (SELECT gdp FROM world WHERE continent = 'Europe' and gdp is not null)

Answer 2

For achieveing desired result you have to try somthing like this:-

SELECT name 
FROM world 
WHERE gdp > ALL (SELECT MAX(gdp) 
                 FROM bbc 
                 WHERE contintent = 'Europe' 
                 AND gdp IS NOT NULL)

and if no countries have GDP as NULL then you can simply remove IS NULL cond.

Hope this can help you.