Query question

Hi ,

I have table that represent a switch activity like this :

|         date                    | state  |
| 2005-04-20 17:00:00 |   0     |
| 2005-04-20 17:00:15 |   0     |
| 2005-04-20 17:00:30 |   1     |
| 2005-04-20 17:00:45 |   1     |
| 2005-04-20 17:01:00 |   1     |
| 2005-04-20 17:01:15 |   0     |
| 2005-04-20 17:01:30 |   0     |
| 2005-04-20 17:01:45 |   0     |

I want to get the date of each states change but i not a sql expert.
Can someone advices me

Thanks