During Db setup sometimes I forget to add my key fields , howerver I can find duplicates in a single table using the following:
SELECT Field1, Field2, Field3, Field4, RecordID
FROM YourTable
WHERE (RecordID IN
(SELECT [RecordID]
FROM [YourTable] AS Tmp
GROUP BY [RecordID]
HAVING COUNT(*) > 1)) AND (RecordID <> 0)
ORDER BY RecordID

With some modification you can utilize this to search for orphand records.