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sql-server 2008  trigger for counting row access.

Posted on 2013-05-19
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Last Modified: 2013-05-25
Hi!

I have a table like this! (UserData)
 itemId, Itemname, ItemUrl,,,,,,,,,


then i have an other table (Accesscounter)
Itemid, NumberOfDOwnload, LatestDownload,,,,,

i  need a trigger into sql-server2008 that updates the Accesscounter everytime
a row in Userdata is accessed.  
so when itemid x in Userdata is accessed it needs to write the itemid into accessCounter and increment number of downloads and the datetime for latestdownload.  
Btw. if the item in AccessCounter already exists it needs to update the row not create a new one!

How would this be done with a trigger? now i deal with it in code but a trigger would be a nicer solution.
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Question by:jamppi
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9 Comments
 
LVL 60

Expert Comment

by:Kevin Cross
ID: 39179667
With SQL 2008, you can use the MERGE feature that can handle the UPDATE or INSERT, depending on existence of match. Therefore, you can have your trigger aggregate the UserData by ItemId to get COUNT of downloads and MAX download date. You can then use the result as the source table and Accesscounter as the target table in the MERGE statement.

MERGE: http://technet.microsoft.com/en-us/library/bb510625.aspx
CREATE TRIGGER: http://msdn.microsoft.com/en-us/library/ms189799(v=sql.105).aspx

Does this make sense?

Please give it a try and post back any questions as well as some sample data and the expected results.

Kevin
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LVL 35

Accepted Solution

by:
David Todd earned 500 total points
ID: 39179823
Hi,

Maybe I'm missing something, but isn't the asker asking for every time the row is selected, as well as inserted/updated/deleted?

The modifications can use a trigger - insert/update/delete - but not the select.

If all access was via stored procedures, then adding this logging would be easy. But I'm not sure how to do the selects without a procedure as an interface.

Regards
  David
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LVL 75

Expert Comment

by:Anthony Perkins
ID: 39179904
How would this be done with a trigger
As David has indicated you cannot have a TRIGGER on a SELECT.
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Author Comment

by:jamppi
ID: 39180520
Acperkins.

So i guess i need some other approach to this then.

/j
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LVL 35

Expert Comment

by:David Todd
ID: 39180540
Hi

Yes.

I pointed out one alternative ...

Regards
  David
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Author Comment

by:jamppi
ID: 39180591
dtodd:

So you suggest that i would create a stored procedure, have the query run against the sproc  and have that in turn update the accesscounter?
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LVL 60

Expert Comment

by:Kevin Cross
ID: 39181355
Yes, I missed you wanted this on SELECT. My understanding is that a simple query of the items should not update a counter that it was downloaded. What if I simply kept refreshing the application (web page) without ever downloading the file? My initial guess was the application would write back a date or a new record whenever the application downloaded the file. Therefore, I agree with others, but I would also look at your application design and definition of a download if it is triggered on a simple SELECT statement.
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Author Comment

by:jamppi
ID: 39181443
ok.  well this is a part of a REST api.
So when the query returns it actually changes the 'Response.ContentType' to Pdf.
that is why i can be somewhat sure about the download process.
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LVL 60

Expert Comment

by:Kevin Cross
ID: 39181465
That makes sense. If you are unable to use the stored procedure idea, then you can see if you can have the web side put a value in database before transferring to view PDF. That way, you can trigger on the INSERT or UPDATE.
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