How do I set up my reference tables?

[DelannaLeonard]

I have a table called Items where I store each item that I ordered. 

Each item has an invoice but each invoice have many items on it so I find myself attaching the same invoice to different items. I don't want to do that.

I want to know how to set up my tables so that these things can happen:

• When I'm in Items table I can add a new invoice/ attach one that is already made.
• When I'm in invoice table I can add an invoice and have an Enumlist of items so that i can choose more than one items to attach to the invoice. 
• I also want the Enumlist to only show items that have not yet had an invoice assigned to it.

Thanks alot for the help in advance.

[SkrOYC]

Just to make sure this is what you really need.

Items are unique for a particular Invoice but can exist without one?
This is like an inventory thing but you just have one item instead of multiple ones of the same -say- SKU?

Thanks

[DelannaLeonard]

Yes items can exist without an invoice but most likely all items will have invoices.

What I'm doing is keeping a record of items I order online: When I make an order of more than one items the seller will provide me an invoice that has all those items on it. 

So in Items[invoice] (the Invoice column in the Items table) I want to be able to upload new invoices from there but also have the option to attach an invoice that is already uploaded.

And from the Invoice table I want to be able to upload an invoice and then choose the multiple items from items table that are on the invoice.