I have a problem that seems similar to this fellow - I just want to display the data slightly differently. I'm pretty terrible with SQL so can't modify it to suit, but perhaps someone else can.

My table looks similar to this (date format is dd/mm/yyyy):

ID  User  Date_start   Role
1   Andy  01/04/2010   A
2   Andy  10/04/2010   B
3   Andy  20/04/2010   A
4   John  02/05/2010   A

I want to show the total number of days that anyone was in a certain role. Users stay in the role until there is another entry into the table. Users can only be in one role at a time. So the summary data would look like this (assuming that the date is 04/05/2010):

A: 26 days
B: 10 days

Thanks for any help :)