Our card authorization decline rate jumped from 2% to 3.5% this week, and customer complaints are up. We have an authorization log where each record has the transaction time, the channel—online or in-store—the merchant category, whether it was declined, and the decline reason. How would you use SQL to pinpoint where the problem is?

我们卡交易的授权拒绝率这周从2%涨到了3.5%，客户投诉也多了。有一张授权记录表，每笔记录了交易时间、渠道是线上还是线下、商户类别、是否被拒和拒绝原因。你怎么用SQL定位问题出在哪？