Not to be casting aspersions on Jeff's fine solution mind you, but I'd probably do it something like this:
WITH PreAggregate AS
(
SELECT OrderNo, SubTotal = SUM(Amount)
FROM #TestTable
GROUP BY OrderNo
)
SELECT a.OrderNo
,Something
,Amount
,SubTotal
FROM #TestTable a
JOIN PreAggregate b ON a.OrderNo = b.OrderNo
ORDER BY OrderNo, Something;
Reference: The Performance of the T-SQL Window Functions [/url]
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