I have 3 tables (tblFreightHeader, tblSalesOrder, tblInvoiceNumber)
tblFreightHeader: FreightHeader_ID (PK), Carrier, Weight, FreightAmount
tblSalesOrder: SalesOrder_ID (PK), FreightHeader_ID (FK), SalesOrderNumber, Customer, SalesOrderAmount
tblInvoiceNumber: InvoiceNumber_ID (PK), SalesOrder_ID (FK), InvoiceNumber, InvoiceAmount
They way it works is that there could be multiple sales order for one freightheader record. There could also be multiple invoice number for one sales order (sometimes sales orders are completed in parts i.e. various invoices).
Should I create a foreign key between tblFreightHeader and tblInvoiceNumber?