setting the where clause

Hi,
I'm am programming in python using the Dabo modules.  www.dabodev.com if your 
interested.  Dabo is a framework that provides an easy way to build desktop 
app's.  To clear a data entry form. I have been setting the where clause 
to "where 1=0".  This of course retrieves 0 records and my form will display 
nothing.  It has been suggested that it might be better to set the where 
clause to a primary key value that does not exist in the table  "where PK 
= -9999999".   

I wonder what you guys think.  How might it effect performance?
-- 
John Fabiani