Lowell has provided you a perfectly good solution to your question. However, you may want to also consider something like the following for performance reasons:
WITH PreAggregate AS
(
SELECT customerid
,sa1=SUM(amount)
,sa2=SUM(CASE WHEN order_date > '2012-01-15' THEN amount ELSE 0 END)
FROM sales_orders
GROUP BY customerid
)
Select customerid, orderid, order_date, amount, sa1, sa2
FROM sales_orders a
JOIN PreAggregate b ON a.customerid = b.customerid;
Reference: The Performance of the T-SQL Window Functions [/url]
Edit: Lowell, please pardon me for originally suggesting that your fine solution was the work of Luis. I didn't get Luis's post until just now. [face-slap]/face-slap]
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St