gistfile1.txt

Here's my sample data set

mysql> SELECT tf.id, tf.authorization_id_response, tf.tran_type FROM transaction_feeds tf;
+-----+---------------------------+-----------+
| id  | authorization_id_response | tran_type |
+-----+---------------------------+-----------+
| 239 | 223672                    | 9120      | 
| 240 | 223672                    | 9220      | 
| 241 | 223673                    | 9120      | 
+-----+---------------------------+-----------+
3 rows in set (0.00 sec)

I'd like to be write a query that will find all items in the table with
tran type 9120 which do not also have another entry in the table with the 
same authorization_id_response.

SELECT id, authorization_id_response, tran_type
FROM transaction_feeds tf
WHERE NOT EXISTS (
  SELECT authorization_id_response
  FROM transaction_feeds
  WHERE id != tf.id
    AND authorization_id_response = tf.authorization_id_response
)