Try this one:
query4:
SELECT Table1.id, Table1.fld1, Table1.fld2, Table1.fld3
FROM Table1
WHERE NOT (Table1.fld1 Is Not Null AND Table1.fld2 Is Not Null AND Table1.fld3 Is Not Null)
OR (Table1.fld1 Is Null AND Table1.fld2 Is Null AND Table1.fld3 Is Null)
And remember, if the field contains a ZLS it is still "empty" but it is not null and will not be treated correctly in the expression
I'm sure there is a better way to do this but I'm done. I've spent enough time on it. I updated the sample database to include the fourth query.