给出一个客户订单表,列为客户ID,订单ID和订单日期,写一个SQL查询,以查找每个客户的第一订单日期.
You can use the MIN() function to find the earliest order date for each customer. Here is an example SQL query:

```
SELECT CustomerID, MIN(OrderDate) AS FirstOrderDate
FROM CustomerOrders
GROUP BY CustomerID;
```

This will group the orders by customer, and select the customer ID along with the earliest order date (aliased as "FirstOrderDate") for each group.