Find the difference between 2 rows (date - same column)

[apervez]

Hi,
I have a table with two columns ID and mydate date type. I need to calculate the difference (number of days) difference between first row date to second and second to third and so on...)
how this can be achieved?

ID mydate DIFF_DAYS
1 01-JAN-13 0
2 05-JAN-13 4
3 14-JAN-13 9
4 15-JAN-13 1

Thanks.