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Richiesta in formato liberoExplain the function of `CROSS APPLY` in the code below: ```sql SELECT customer.CustomerId, customer.CustomerName, ord.* FROM customers customer CROSS APPLY ( SELECT SUM(order.quantity) as TotalQuantity FROM orders order WHERE order.CustomerId = customer.CustomerId ) ord; ``` RispostaThe `CROSS APPLY` operator in the provided SQL code performs a lateral join, which allows you to access data from a related table for each row in the outer table. In this case, the outer table is the `customers` table, and the related table is the `orders` table. The `CROSS APPLY` operator is used to calculate the total quantity of orders for each customer. The subquery within the `CROSS APPLY` operator calculates the sum of the `quantity` column from the `orders` table for each customer. The result of the subquery is then assigned to the alias `ord`, which is used to access the calculated total quantity in the outer query. The output of the query will be a table that contains the following columns: * `CustomerId` * `CustomerName` * `TotalQuantity` For each row in the `customers` table, the query will calculate the total quantity of orders placed by that customer. |
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