给出一个客户订单表,列 OrderID,客户ID,订单日期和订单金额,写一个更新声明,增加订单金额的5%所有订单的客户,他们已经放置至少5订单在过去一年.
Assuming that the name of the table is "orders" and the date range for the past year is defined as the current date minus 365 days, the UPDATE statement would be:

```
UPDATE orders
SET OrderAmount = OrderAmount * 1.05
WHERE CustomerID IN (
  SELECT CustomerID
  FROM orders
  WHERE OrderDate >= DATEADD(day, -365, CURRENT_TIMESTAMP)
  GROUP BY CustomerID
  HAVING COUNT(OrderID) >= 5
);
```

This statement uses a subquery to identify the customers who have placed at least 5 orders in the past year, and then updates the OrderAmount for their orders by multiplying the existing OrderAmount by 1.05, which represents a 5% increase.