Displaying records that aren't found on a related table
I use a self-join table to link records into "clusters" of records, which are similar to the original records but are linked back to the first-level records with a simple table row:
_fkLinkedObservationID | _fkObservationID
Where ObservationID is the first-tier record and LinkedObservationID is the second-tier.
My users would like to see first-tier records that are not part of any second-tier record. I basically will have to display the list of record IDs that DO NOT appear in the _fkObservationID column, but I don't know the best way to go about doing this.
Thanks in advance for any help.