I have a situation where I need to find time spans between value changes. I tried a simple group by clause but it eliminates overlapping changes. Consider the following example:

create table #items (
      code varchar(4)
    , class varchar(4)
    , txdate datetime
)

insert into #items (code, class, txdate) values ('A', 'C', '2010-01-01');
insert into #items (code, class, txdate) values ('A', 'C', '2010-01-02');
insert into #items (code, class, txdate) values ('A', 'C', '2010-01-03');
insert into #items (code, class, txdate) values ('A', 'D', '2010-01-04');
insert into #items (code, class, txdate) values ('A', 'D', '2010-01-05');
insert into #items (code, class, txdate) values ('A', 'C', '2010-01-06');
insert into #items (code, class, txdate) values ('A', 'C', '2010-01-07');
insert into #items (code, class, txdate) values ('A', 'D', '2010-01-08');
insert into #items (code, class, txdate) values ('A', 'D', '2010-01-09');

select code
, class
, min(txdate) mindate
, max(txdate) maxdate
from #items
group by code, class

This returns the following results (notice the overlapping date ranges):

|code|class|mindate   |maxdate   |
----------------------------------
|A   |C    |2010-01-01|2010-01-07|
|A   |D    |2010-01-04|2010-01-09|

I would like to have the query return the following:

|code|class|mindate   |maxdate   |
----------------------------------
|A   |C    |2010-01-01|2010-01-03|
|A   |D    |2010-01-04|2010-01-05|
|A   |C    |2010-01-06|2010-01-07|
|A   |D    |2010-01-08|2010-01-09|

Any ideas and suggestions?