Feat/authors/guilhermevalenca

authors/Guilhermevalenca/01.sql

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+select * from products;

authors/Guilhermevalenca/02.sql

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+select
+	products.*,
+	suppliers.company_name
+from
+	products
+left join 
+	suppliers
+	on products.supplier_id = suppliers.supplier_id;

authors/Guilhermevalenca/03.sql

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+select 
+	*,
+	customers.company_name,
+	concat(employees.first_name, ' ', employees.last_name) as full_name
+from 
+	orders
+left join
+	customers on orders.customer_id = customers.customer.id
+left join
+	employees on orders.employee_id = employees.employee.id;

authors/Guilhermevalenca/04.sql

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+select 
+	*,
+	categories.category_name,
+	suppliers.company_name
+from
+	products
+left join
+	categories on products.category_id = categories.category_id
+left join 
+	suppliers on products.supplier_id = suppliers.supplier_id;

authors/Guilhermevalenca/05.sql

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+select 
+	customers.company_name,
+	count(orders.order_id) as total_orders 
+from
+	customers
+left join
+	orders on customers.customer_id = orders.customer_id
+group by customers.company_name;

authors/Guilhermevalenca/06.sql

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+select 
+	concat(employees.first_name, ' ', employees.last_name) as name,
+	'R$ ' || round( cast( sum(order_details.quantity * order_details.unit_price) as numeric), 2) as total_sales
+from 
+	employees
+left join 
+	orders on orders.employee_id = employees.employee_id
+left join
+	order_details on order_details.order_id = orders.order_id
+group by
+	name;

authors/Guilhermevalenca/07.sql

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+select
+	categories.category_name,
+	'R$ ' || trunc( cast( avg(products.unit_price) as numeric), 2) as average_pre_product
+from 
+	categories
+left join 
+	products on categories.category_id = products.category_id
+group by
+	categories.category_name;

authors/Guilhermevalenca/08.sql

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+select
+	customers.company_name
+from
+	customers
+left join 
+	orders on orders.customer_id = customers.customer_id
+where
+	orders.order_id is null
+group by
+	customers.company_name;