Form and subform not showing duplicates for payments

[Joe8915]

Need a thought process here.

I have a form with all the information for a contractor
I have subform that is link to the contractor showing all payments.
On my subform I have field for Invoice number.
What I am trying to accomplish is not duplicating any Invoice numbers.

I was thinking about a IIF statement, but that will not work. How else could I do it?

Thanks all

 

[Joe8915]

I think I found my answer
http://www.access-programmers.co.uk/forums/showthread.php?t=200376&highlight=duplicate

Being new at VBA I really don't know how I would insert the correct fields. The table I would use is called tblproclog, the form is called frmPE, the subform is called frmlPESubform. The field in the subform is called InvoiceNumber.

Just in case anyone would like to take a stab at it