No unique index found for the referenced field of the primary table

[bernese]

I have an assignment where I need to design a database with special instructions. Within the db design are 2 tables: one table (Purchase Orders) with 2 primary fields identified (Purchase number and Computer Part #), the second Table is the Cash Disbursements Table that has Purchase number as a foreign key. I am trying to create relationships between these 2 tables using the Purchase Number key, but get the error noted above in the title. I do see that some of the Purchase numbers are duplicated in my tables. How do I get around this and design the table as requested in the instructions: with Purchase Orders Table having both Purchase Number and Computer Part Number as primary keys and linking the Purchase Number to the foreign key in the Cash Disbursements Table?

Any assistance would be greatly appreciated.

 

[Micron]

You are probably trying to enforce referential integrity, which you cannot do in this situation. If you were not told to do that, then don't and the message should go away.
For what it's worth, the assignment requirements seem bizzare. A PO table should be a header with PO number, create date, status, etc. etc. A PO line items table is where part numbers or their reference ID's should go.