Tri of field and select only one occur

[steve austin]

Hi,

I have this data

a | b | c |
+------+------+------+
| 3 | 1 | 2 |
| 3 | 2 | 1 |
| 3 | 2 | 2 |
| 13 | 4 | 7 |

and i would like to select only on occur from the different field like below
a | b | c |
+------+------+------+
| 3 | 2 | 2 |
| 13 | 4 | 7 |
| 3 | 2 | 1 |

Then the first line (or the second) must dissapear how can i do taht thanks