We have a credit card transaction table where each record has the customer, transaction date and amount, and refunds are stored as negative amounts. For example, customer 101 had two purchases of 600 and 500 last month plus a refund of 200. Your manager wants the number of customers whose net spend last month exceeded 1,000 dollars. How would you write the SQL, and does customer 101 count?

有一张信用卡交易表，每笔记录了客户、交易日期和金额，退款记为负数。比如客户101上个月消费了600和500两笔，又有一笔200的退款。老板想知道上个月净消费超过1000美元的客户有多少个，你怎么写SQL？客户101算不算进去？