Adds the unique key field of the primary record type of this query to the QueryFieldDefs object.
Creates and adds to the collection a QueryFieldDef object that makes up a unique key field. This field is a concatenation, into a single string, of all the fields that make up a unique key (if there are more than one). For example, if you have a unique key of first-name + last-name, this would generate SQL like (syntax varies by vendor):
select concat(first_name, last_name) from defect.
You would get back a single result column with values like "Joe Jones".