Every night we load the previous day's credit card transactions into the warehouse. For the past week it's been around 100,000 transactions a day, but today's load has only 60,000, and the job still shows success. How would you build an automated SQL check to catch days like this, and how would you set the threshold?

我们每天凌晨把前一天的信用卡交易加载进数仓。过去一周每天都在10万笔上下，今天只有6万笔，但任务显示成功。你会怎么用SQL做一个自动监控把这种异常日抓出来？阈值怎么定？