MAX or ALL in sql - mysql

Question

I'm doing this question:
Which countries have a GDP greater than every country in Europe? [Give the name only.] (Some countries may have NULL gdp values)
The suggested answer from the website is:
SELECT name
FROM world
WHERE GDP >= ALL(SELECT GDP
FROM world
WHERE population>0 AND continent = 'Europe' )
Here it uses ALL keyword , and need to take care of the null value using WHERE population >0
My solution is like this:
SELECT name
FROM world
WHERE GDP >= (SELECT MAX(GDP)
FROM world
WHERE continent = 'Europe')
I use the MAX keyword and it seems that in this case we don't need to considering taking care of NULL value
Is my solution right? What's the trade-off of the two solutions?

Answer 1

Aggregate functions like MAX ignore NULL-values, so the meaning of condition
... WHERE GDP >= (SELECT MAX(GDP) FROM world WHERE continent = 'Europe')
is: it is true, if GDP is greater or equal than the GDP of every european country that has a GDP defined.
And it is equivalent to a condition like:
GDP >= ALL(SELECT GDP FROM world WHERE continent = 'Europe' and GDP is not null)
So it this is what you want to achieve (and I would interpret the exercise that way), then your approach is correct.

Answer 2

There is a very small content available regarding the performance of both. The page is available at MySQL docs.
MySQL rewrites IN, ALL, ANY, and SOME subqueries in an attempt to take advantage of the possibility that the select-list
columns in the subquery are indexed.
MySQL enhances expressions of the following form with an expression involving MIN() or MAX(), unless NULL values or empty sets are
involved:
value {ALL|ANY|SOME} {> | < | >= | <=} (uncorrelated subquery)
For example, this WHERE clause:
WHERE 5 > ALL (SELECT x FROM t)
might be treated by the optimizer like this:
WHERE 5 > (SELECT MAX(x) FROM t)
Therefore; for your particular case, the website mentions using ALL because of the possible NULL values in data. If that were not the case, you can replace ALL with MAX as stated above.