When Acoustic Campaign evaluates relational table criteria, the system is looking for records that match the criteria specified. This means that if you specify 'Field XYZ is Blank/Empty', you see only records where that field has no value. What if you want to find only contacts who have no corresponding data in the relational table at all?
To find these records, change your relational table criteria into a not statement. This allows you to return records that do not match the specified criteria. You should use the keyed value for the table as the basis for the criteria.
For example, if your table is keyed on Purchase Number, your criteria should look something like:
In relational table: Orders when Purchase Number is not blank
This returns all contacts who have a record in the relational table with a Purchase Number. Now you need to make this a not statement. The method depends on what type of query you use.
This option returns all contacts who do not match the provided criteria.