Can this be done with sql?

In my database i have values recorded in one minute intervals. I would
like a query that can get me results for other time intervals. For
example - return maximum value in each 3 minute interval. Any ideas
how i can do this with sql? I tried writing a procedure in plsql but i
am told it does not support tuples as output. I can get the all the
one minute intervals and process them to get me three minute intervals
in my application but i would rather not do the expensive call for the
one minute intervals in the first place due to the large number of
data. any ideas?

thanks