scalar function brings performance problems

Hi experts, a friend told me that a scalar function brings performance problems because it runs row by row, is that true? but does not use scalar function then how would you do?. ULR know of any that speaks this kind of thing
enrique_aeoAsked:
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coalanexpertCommented:
Depending on the cost of the query that the function actually executes it might affect performance. The book says to try to use inline table functions instead, but again if your scalar function is simple, no need to complicate things.
Here a reference on how to use inline table valued functions

http://stackoverflow.com/questions/800017/why-do-sql-server-scalar-valued-functions-get-slower

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enrique_aeoAuthor Commented:
I have this function
CREATE FUNCTION dbo.SumVta(@ProductID int)
RETURNS int
AS
BEGIN
  DECLARE @ret int
  SELECT @ret = SUM(Quantity)
  FROM [Order Details]
  WHERE ProductID = @ProductID
  IF (@ret IS NULL)
  SET @ret = 0
RETURN @ret
END
how could I make a table inline Functions?
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
>because it runs row by row

yes.

your function would require a (clustered) index on ProductID on table order details to run fastest, unless you can build up the "sum_quantity" column in the products table directly, and keep that updated with triggers (real-time) or regular jobs (scheduled updates)
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joriszwaenepoelCommented:
I think you can solve this with a JOIN and a GROUP BY:

Something like:

SELECT Order.OrderID, OD.ProductID, SUM(OD.Quantity) AS SumVta
FROM [Order]
INNER JOIN [Order Details] OD
ON Order.OrderID = OD.OrderID
GROUP BY Order.OrderID, OD.ProductID

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Microsoft SQL Server 2008

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