We want to track the 90-day activation rate for new cards. One table has each customer's account open date, and another has every transaction with customer, date and amount, where refunds are negative. For example, customer 101 only has a refund of minus 50 on day 10, and customer 102 makes a first purchase on day 100. How would you define activation, do these two count, and how would you write the SQL?

我们想看新卡的90天激活率。有一张开卡表记录每个客户的开卡日期，一张交易表记录每笔交易的客户、日期和金额，退款记为负数。比如客户101开卡第10天只有一笔负50的退款，客户102第100天才首刷。你怎么定义激活率？这两个人算不算？SQL怎么写？