Store calculations in a table or use computed columns?

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Store calculations in a table or use computed columns?

tobbe 47526

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Points: 18
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June 3, 2010 at 6:09 am

#219669

I'm working on a Silverlight / WCF project and I'm now in need of some SQL guidance from you people that know SQL inside out.
I have reached a point in the project where I need to give the user the ability to create certain calculations that is going to be used for validating all the data that goes into the database.
To give a short explanation:
- Table A contains data concerning electrical consumption
- Table B contains data concerning heat consumption
- The user adds a calculation [Table A].[Column 1] - [Table B].[Column 4] and a max value that this calculation may have. A service would later use this calculation to match it against the set max-value.
From my POW, this can me done in two ways, either store the calculations instruction-wise (eg. a table with all the necessary details that is needed for a service to fetch all the needed data and do the calculations off-site) OR one could create a view with computed columns which does this automatically.
Can someone please give me some pointers in which direction I should be going? Should I implement this the view-way (generate views through my application that does the calculations) or should I somehow store the instructions for the calculations in a table and use a service which does all the calculations and checks (would poll the database a lot more than going the view way).
Are there any other alternatives which I should take into consideration? Has anyone encountered this before and how have you solved it?
/Tobias

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Lowell SSC Guru Points: 323546 More actions · Answer 1

the devil is in the details, but here's my two cents:

use computed columns or a view which does the computation for you whenever possible.

i don't know if you've ever tried it, but storing a formula in a field, and then trying to execute the value of the field to get the results is a real pain in the... whatever.

try it with a simple example...

declare @MyCalculation varchar(30)

SET @MyCalculation ='SELECT 1 + 2+ 3'

EXEC (@MyCalculation)

--or worse COLUMNA + COLUMNB

see if you can get the results back...it's a pain.

Lowell

--help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!

tobbe 47526 Grasshopper Points: 18 More actions · Answer 2

Thanks Lowell, I'll start working on using computed columns.

If anyone else pictures an even better way when reading this post, please share your ideas 🙂

Jeff Moden SSC Guru Points: 1004641 More actions · Answer 3

As Yogi Bera used to say, "When you come to a fork in the road, take it.". If you can suscessfully create a computed column, try to make it a "persisted" computed column.

--Jeff Moden

RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

Change is inevitable... Change for the better is not.

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