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USE world_x; SELECT * FROM city; SELECT * FROM country; SELECT * FROM countryinfo; SELECT * FROM countrylanguage; -- Proyección SELECT id, name, countrycode, district, info FROM city; -- Proyección SELECT countrycode, language, percentage FROM countrylanguage; -- Seleccion SELECT countrycode, language, percentage FROM countrylanguage WHERE percentage>10; -- Union: SELECT language, percentage FROM countrylanguage UNION SELECT countrycode, info FROM city; SELECT capital, code2 FROM country UNION SELECT district, name FROM city; -- join: SELECT * FROM country JOIN city ON country.code = city.countrycode; SELECT * FROM country JOIN city ON country.capital = city.id; SELECT country.name, city.name FROM country JOIN city ON country.capital = city.id; SELECT country.name, countrylanguage.language, countrylanguage.percentage FROM country JOIN countrylanguage ON country.code = countrylanguage.countrycode WHERE percentage>20 ORDER BY percentage DESC;
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