You have two Excel sheets: a transaction sheet with customer ID and amount on each row, and a customer sheet with customer ID and card tier. Customer 101 has two transactions of 200 and 300 and is Platinum; customer 205 has one transaction of 150 but doesn't appear in the customer sheet. How do you bring card tier onto the transaction sheet, what shows up for 205, and how do you handle it?

你手上有两张Excel表：一张交易明细，每行有客户编号和交易金额；一张客户表，记录客户编号和卡等级。客户101有200和300两笔交易，是白金卡；客户205有一笔150，但客户表里查不到他。你怎么把卡等级带到交易表上？205那一行会显示什么，你怎么处理？