Mike,

The question mark indicates a parameter (as in a view). However in this case you can drop "?" and result will be the same.
Also it's better to put a field in the WHERE condition on the left.

* If ThisForm.Customer is numeric/integer
    (ThisForm.Customer = 0 or  Ordhead.customerid = ThisForm.Customer)
* If ThisForm.Customer is character (nn is the size of Ordhead.customerid field)
    (ThisForm.Customer == SPACE(nn) or  Ordhead.customerid = ThisForm.Customer) 

>In a SQL select statement. (original code VFP 5) I came across the code below as part of the WHERE clause
>

>(Empty(?ThisForm.Customer) or  ?ThisForm.Customer= Ordhead.customerid)
>

>
>As stated previously, empty is not rushmore optimizable, therefore how do I change this to return the same info. I am rewriting the queries in VFP 9 and wish to get the same results.