with pivot_data as
  (
    select user_id, EXTRACT(hour from dstamp) as somehour, sum(update_qty) as someqty
    from inventory_transaction
    where TO_CHAR(dstamp,'DD/MM/YYYY hh:mm') between '16/09/2015 06:00' and '17/09/2015 05:59'
    group by user_id, EXTRACT(hour from dstamp)
    Order By EXTRACT(hour from dstamp)
  )
select * 
from pivot_data
  PIVOT (
          sum(update_qty)        --<-- pivot_clause
          FOR EXTRACT(hour from dstamp)        --<-- pivot_for_clause
          IN  (11,12,13,14)   --<-- pivot_in_clause
         );

SQL> SELECT 1 FROM dual
  2  WHERE TO_CHAR(to_date('16/10/2500 02:00', 'DD/MM/YYYY hh:mi'),'DD/MM/YYYY hh:mi') between '16/09/2015 06:00' and '17/09/2015 05:59';
 
         1
----------
         1

SQL> SELECT 1 FROM dual
WHERE to_date('16/10/2500 02:00', 'DD/MM/YYYY hh:mi') between to_date('16/09/2015 06:00','DD/MM/YYYY hh:mi') and to_date('17/09/2015 05:59','DD/MM/YYYY hh:mi');  2 

no rows selected