SQL Server Cumulative Sum by Group

I have a table (SQL Server 2005) of this format:

dummy_id, date_registered, item_id, quantity, price

and I want to add a new column (cumulative) which calculates the cumulative totals of each item_id order by date_registered as shown:

dummy_id  date_registered  item_id  quantity    price   cumulative

1           2013-07-01        100      10        34.5       10

2           2013-07-01        145       8        2.3         8

3           2013-07-11        100      20        34.5       30

4           2013-07-23        100      15        34.5       45

5           2013-07-24        145      10        34.5       18

Thanx in advance

In SQL Server 2005, I would do this using a correlated subquery:

select dummy_id, date_registered, item_id, quantity, price,
       (select sum(quantity)
        from t t2
        where t2.item_id = t.item_id and
              t2.date_registered <= t.date_registered
       ) as cumulative
from table t;

If you actually want to add this into a table, you need to alter the table to add the column and then do an update. If the table has inserts and updates, you will need to add a trigger to keep it up-to-date. Getting it through a query is definitely easier.

In SQL Server 2012, you can do this using the syntax:

select dummy_id, date_registered, item_id, quantity, price,
       sum(quantity) over (partition by item_id order by date_registered) as cumulative
from table t;