Magento MySql Query to fetch List of first time buyers

I Would like to produce a MySql Query to be execute on sales_flat_order table. and to fetch a list of customers that has made their first order between dates.

select customer_id from sales_flat_order where 
created_at between '1/1/2013' and '30/1/2013'
and (this is the first time that the customer has made an order. 
     no records for this customer before the dates)

Thanks

Solution

First, get every customer's earliest order date:

SELECT
    customer_id,
    MIN(entity_id) AS entity_id,
    MIN(increment_id) AS increment_id,
    MIN(created_at) AS created_at
FROM sales_flat_order
GROUP BY customer_id

Results:

+-------------+-----------+--------------+---------------------+
| customer_id | entity_id | increment_id | created_at          |
+-------------+-----------+--------------+---------------------+
|           1 |         1 | 100000001    | 2012-04-27 22:43:27 |
|           2 |        15 | 100000015    | 2012-05-10 14:43:27 |
+-------------+-----------+--------------+---------------------+

Note: The above assumes that the smallest entity_id for a customer will match the earliest created_at for a customer.

Building on this, you can join with the orders:

SELECT o.* FROM sales_flat_order AS o
JOIN (
    SELECT
        customer_id,
        MIN(entity_id) AS entity_id,
        MIN(created_at) AS created_at
    FROM sales_flat_order
    GROUP BY customer_id
) AS first ON first.entity_id = o.entity_id
WHERE
    first.created_at BETWEEN '2013-01-01' AND '2013-01-30';