MySQL - seleccionar valores distintos de varias columnas

mysql> SELECT * FROM tabla;

+------+---------+----------+----------+

| id   | id_dato | columna1 | columna2 |

+------+---------+----------+----------+

|    1 |       1 | estuche  | grande   |

|    2 |       1 | estuche  | mediano  |

|    3 |       2 | otro     | grande   |

|    4 |       2 | otro     | mediano  |

|    5 |       2 | otro     | chico    |

+------+---------+----------+----------+

5 rows in set (0.05 sec)

mysql> SELECT

    ->   id,

    ->   id_dato,

    ->   CASE WHEN NOT EXISTS

    ->   ( SELECT id

    ->     FROM tabla T2

    ->     WHERE T2.id_dato = T1.id_dato

    ->           AND T2.id < T1.id

    ->   ) THEN columna1 ELSE NULL END columna1,

    ->   columna2

    -> FROM tabla T1

    -> ORDER BY T1.id;

+------+---------+----------+----------+

| id   | id_dato | columna1 | columna2 |

+------+---------+----------+----------+

|    1 |       1 | estuche  | grande   |

|    2 |       1 | NULL     | mediano  |

|    3 |       2 | otro     | grande   |

|    4 |       2 | NULL     | mediano  |

|    5 |       2 | NULL     | chico    |

+------+---------+----------+----------+

5 rows in set (0.00 sec)