It's month-end reconciliation. Our core system shows 10,000 transactions totaling 5 million this month; the settlement file from the processor shows 9,980 transactions totaling 4.98 million. Both have transaction ID and amount. That's a gap of 20 transactions and 20K. How would you pinpoint the differences in Excel or SQL, and what could be causing them?

月底对账，核心系统导出当月交易10000笔、合计500万；清算方的文件是9980笔、合计498万，两份都有交易编号和金额。差了20笔、2万块，你会怎么在Excel或SQL里定位差异？可能是什么原因？