DELETE FROM IdentifierMapperStorageObject WHERE InternalId = ExternalId;
DELETE FROM IdentifierMapperStorageObject
WHERE id IN
   ( SELECT IMSO.Id
        FROM IdentifierMapperStorageObject AS IMSO
     LEFT JOIN
      ( SELECT max(Row_Number) AS dontdelete,
               max(CONVERT(BIGINT, CONVERT (VARBINARY(36), IM.id, 1))) AS rowid,
               IM.[QualifiedName]
       FROM IdentifierMapperStorageObject AS IM
       JOIN
         ( SELECT count(r.id) AS Row_Number,s.id
                    FROM [IdentifierMapperStorageObject] AS s
           JOIN [IdentifierMapperStorageObject] AS r ON s.id >= r.id
                    GROUP BY s.id) AS RowNum ON IM.id = RowNum.Id
       JOIN
         ( SELECT [QualifiedName],count(*) AS cnt
                    FROM [IdentifierMapperStorageObject]
                    GROUP BY[QualifiedName]
                    HAVING count(id) > 1  ) AS dupsCount ON IM.[QualifiedName] = dupsCount.[QualifiedName]
             GROUP BY IM.QualifiedName ) AS recordsToKeep ON recordsToKeep.[QualifiedName] = IMSO.[QualifiedName] AND
                                                                                               recordsToKeep.rowid <> CONVERT(BIGINT, CONVERT (VARBINARY(36), IMSO.id, 1))
        WHERE dontdelete IS NOT NULL);