The Relation Only constituency appears on constituent records when a record has no other constituencies, and has a relationship with another constituent in the database. It is automatically added or removed from records as appropriate.
However, it is not possible to query on this constituency - when it is selected as a filter, 0 results are returned in query. If users attempt to output constituencies for records with this Relation Only constituency, the constituency is not listed in the output.
Use the Constituencies (Stored Values) node in Query. For additional information on this feature, review the new features for 4.0 Service pack 6: