запросы:
1
SELECT a.name,a.gdp, b.name, b.gdp
FROM Countries as a JOIN (Select names, gdp From countries as b WHERE b.continent LIKE 'Europe') ON a.gdp > b.gdb
WHERE a.continent NOT LIKE 'Europe'
2
SELECT continent,COUNT()
FROM Countries
WHERE population >= 10000000
GROUP BY continent
3
SELECT continent
FROM Countries
GROUP BY continent HAVING AVG( gdb) > ( SELECT AVG(gdb) FROM Countries)