Combo Box that combines multiple row source codes

[WiscCard]

I have a Yes/No combo box that is based on a table that uses -1, 0 to return those values.
I use the following SQL in RowSource to change that -1, 0 into a Yes/No:

SELECT DISTINCT CUSTOMERS.CONTRACT, IIf([CONTRACT]=-1,"Yes","No") AS YN_Value FROM CUSTOMERS;

However, all my other combo boxes have an All option that was added through SQL RowSource coding like this:

SELECT CONTRACT As Filter, CONTRACT FROM CUSTOMERS UNION SELECT "*" As Filter ," All" As CONTRACT FROM CUSTOMERS ORDER BY CONTRACT;

What I need to do is combine these two row source SQL's into one that will show All, Yes, No.

Any Suggestions?

[NeoPa]

You are simply setting up a ComboBox with three entries right (All; Yes; No)?
"All" should return "*", "Yes" should return -1 (TRUE; YES; etc); "No" should return 0 (FALSE; NO; etc)?