Frustrated In Ohio

Folks, I've been trying to extract the minimum and maximum date from the following query:

select top 27 calendar_day.date_value from calendar_day where calendar_day.date_value < current_date() and calendar_day.insession = 1 order by calendar_day.date_value desc

When I then turn this into a derived table and try to extract the minimum/maximum dates, I get the actual minimum/maximum dates of the whole table rather than the result set from the derived table, so obviously it's an aggregate problem. I'm at a loss to figure out how to pull these two dates out and would appreciate any help from more seasoned SQL folks than me.

Thanks,

David

P.S. I'm using SYBASE SQL