Expliquer un extrait de code SQL.
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Vous pouvez interroger un modèle directement et tester les résultats renvoyés lors de l'utilisation de différentes valeurs de paramètre en utilisant la console Cloud ou en appelant directement l'API Vertex AI.
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Invite forme libre
Explain 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;
```
Réponse
The `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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