Oracle: how to “group by” over a range?

Question

If I have a table like this:

pkey   age
----   ---
   1     8
   2     5
   3    12
   4    12
   5    22

I can \"group by\" to get a count

Answer 1

I had to group data by how many transactions appeared in an hour. I did this by extracting the hour from the timestamp:

select extract(hour from transaction_time) as hour
      ,count(*)
from   table
where  transaction_date='01-jan-2000'
group by
       extract(hour from transaction_time)
order by
       extract(hour from transaction_time) asc
;

Giving output:

HOUR COUNT(*)
---- --------
   1     9199 
   2     9167 
   3     9997 
   4     7218

As you can see this gives a nice easy way of grouping the number of records per hour.