我正在为客户创建发票表。有时他们必须向我发送佣金，或者有时我向他们发送费用（账户余额）。这种情况下如何设计发票表？
我想出了这个解决方案，我不确定这是否正确或替代方法是什么？
tbl_invoice
- invoice_id (PK)
- order_id (FK)
- invoice_date
- amount (copy the price from tbl_order.total table)
- status (Invoice Sent, Cancelled, Amount Received, Amount Sent)
tbl_Payments
- invoice_id (FK)
- amount_received (recieved commission fees from customer)
- amount_sent (sent fees to customer)
- date_received
- date_sent
如果 tbl_invoice.amount 为 -30.00，则意味着客户会将费用寄给我。
如果 tbl_invoice.amount 是 30.00，那么我将向客户发送费用。
我需要 tbl_invoice.amount 字段吗？