SELECT `Code` FROM country WHERE `Name` = 'Armenia';
SELECT * FROM city WHERE `CountryCode` = 'ARM';

SELECT * FROM city 
	WHERE `CountryCode` IN (
		SELECT `Code` FROM country WHERE `Name` IN ('Armenia', 'Argentina')
	);
	
SELECT `CountryCode` FROM countrylanguage  WHERE `Language` = 'English' AND `IsOfficial` = 'T';

SELECT `Code`, `Name` FROM country WHERE `Code` IN (
	SELECT `CountryCode` FROM countrylanguage  WHERE `Language` = 'English' AND `IsOfficial` = 'T'
);