[ADD] JOINS module with classes, resources and tasks

Author: stivenramireza

classes/16-union.sql

@@ -0,0 +1,11 @@
+SELECT *
+FROM continent;
+
+SELECT code, name, '123'
+FROM continent
+WHERE name LIKE '%America'
+UNION
+SELECT code, name, 'Another thing'
+FROM continent
+WHERE code IN (3, 5)
+ORDER BY name ASC;

classes/17-where.sql

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+SELECT *
+FROM country;
+
+SELECT 
+	a.name AS country, 
+	b.name AS continent
+FROM country AS a, continent AS b
+WHERE a.continent = b.code
+ORDER BY b.name ASC;

classes/18-inner-join.sql

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+SELECT *
+FROM country;
+
+SELECT
+	a.name AS country,
+	b.name AS continent
+FROM country AS a
+INNER JOIN continent AS b ON b.code = a.continent
+ORDER BY b.name ASC;

classes/20-alter-sequence.sql

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+SELECT *
+FROM continent;
+
+ALTER SEQUENCE continent_code_seq RESTART WITH 10;
+
+INSERT INTO continent (name)
+VALUES ('North Asia');

classes/21-full-outer-join.sql

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+SELECT *
+FROM continent;
+
+INSERT INTO continent (name)
+VALUES ('Central Asia'), ('South Asia');
+
+-- country a (name, continent)
+-- continent b (name)
+SELECT
+	a.name AS country,
+	a.continent AS continent_code,
+	b.name AS continent_name
+FROM country AS a
+FULL OUTER JOIN continent AS b ON b.code = a.continent
+ORDER BY a.name DESC;

classes/22-right-outer-join.sql

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+SELECT *
+FROM continent;
+
+SELECT
+	a.name AS country,
+	a.continent AS continent_code,
+	b.name AS continent_name
+FROM country AS a
+RIGHT JOIN continent AS b ON b.code = a.continent
+WHERE a.continent IS NULL;

classes/23-aggregations-joins.sql

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+SELECT 
+	b.name AS continent, 
+	COUNT(*) AS count
+FROM country AS a
+INNER JOIN continent AS b ON b.code = a.continent
+GROUP BY b.name
+UNION
+SELECT 
+	b.name AS continent, 
+	0 AS count
+FROM country AS a
+RIGHT JOIN continent AS b ON b.code = a.continent
+WHERE a.continent IS NULL
+GROUP BY b.name
+ORDER BY count ASC;