Revise paste 16. Monasteries by Country

CREATE TABLE monasteries(
	id SERIAL PRIMARY KEY,
	monastery_name VARCHAR(255),
	country_code CHAR(2)
);

INSERT INTO monasteries(monastery_name, country_code)
VALUES
	('Rila Monastery "St. Ivan of Rila"', 'BG'),
	('Bachkovo Monastery "Virgin Mary"', 'BG'),
	('Troyan Monastery "Holy Mother''s Assumption"', 'BG'),
	('Kopan Monastery', 'NP'),
	('Thrangu Tashi Yangtse Monastery', 'NP'),
	('Shechen Tennyi Dargyeling Monastery', 'NP'),
	('Benchen Monastery', 'NP'),
	('Southern Shaolin Monastery', 'CN'),
	('Dabei Monastery', 'CN'),
	('Wa Sau Toi', 'CN'),
	('Lhunshigyia Monastery', 'CN'),
	('Rakya Monastery', 'CN'),
	('Monasteries of Meteora', 'GR'),
	('The Holy Monastery of Stavronikita', 'GR'),
	('Taung Kalat Monastery', 'MM'),
	('Pa-Auk Forest Monastery', 'MM'),
	('Taktsang Palphug Monastery', 'BT'),
	('Sümela Monastery', 'TR');
	
ALTER TABLE countries
ADD COLUMN 
	three_rivers BOOLEAN DEFAULT FALSE;
	
UPDATE
	countries
	
SET three_rivers = (
	SELECT
		COUNT(*) >= 3
	FROM
		countries_rivers AS cr
	WHERE
		cr.country_code = countries.country_code
);

SELECT
	m.monastery_name AS monastery,
	c.country_name AS country
FROM
	monasteries AS m
JOIN
	countries AS c
USING
	(country_code)
WHERE
	NOT three_rivers
ORDER BY
	monastery_name;