title: Invoice table design
body: <p>I am creating an invoice table for the customers. Sometime they will have to send me the commission fees or sometime I send them fees (account balance). How to design a invoice table in this situation?</p>
  
  <p>I have came up with this solution, im not sure if this is correct or what is the alternative way?</p>
  
  <pre><code>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
  </code></pre>
  
  <p>if the tbl_invoice.amount is -30.00 that mean customer will send me the fees.</p>
  
  <p>if the tbl_invoice.amount is 30.00 then I will send the customer the fees.</p>
  
  <p>Do I need tbl_invoice.amount field?</p>
  
  <p>If you could redesign my tables how it should be that be great. </p>