If Update() in a trigger

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If Update() in a trigger

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dean.giberson 64357

Posted Monday, September 17, 2012 2:50 PM

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I have a question that I thought I knew the answer to but I am now not sure. When in a trigger, suppose there are 10 rows in the inserted table. 3 rows have one column(call it A) updated and 7 rows have another column (call it B) updated. If code is entered in the trigger that states If Updated(A) begin ... end will the actions between the begin and end be executed on all 10 rows or only the 3 with the column A updated?

Post #1360457

GilaMonster

Posted Monday, September 17, 2012 3:06 PM

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A trigger fires once only for an operation. All the rows affected by the insert/update/delete will be in the inserted and/or deleted tables.

Gail Shaw
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SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Post #1360466

Jeff Moden

Posted Monday, September 17, 2012 6:32 PM

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dean.giberson 64357 (9/17/2012)

In a single insert or update of all 10 rows for the above, all 10 rows will respond to the IF UPDATED(A) because IF UPDATED() simply checks to see if anything in the whole column for the whole statement was affected.

--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."

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Post #1360512

dean.giberson 64357

Posted Tuesday, September 18, 2012 5:37 AM

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Thanks for the reply. So I am clear on the answer, whatever the processing is between the begin and end will be executed because the system is only checking if column A has been updated for any of the rows in the inserted table so even if only one of the 10 rows had column A updated all 10 rows would still be processed. Am I correct?

Post #1360702

GilaMonster

Posted Tuesday, September 18, 2012 5:54 AM

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Not quite...
It's checking whether ColumnA was one of the columns specified in the SET clause of the update statement.

UPDATE Tbl SET ColumnA = ColumnA

If you had an update trigger on Tbl checking for UPDATE(ColumnA), it would be true for that update statement, even though no rows have the value of ColumnA changed.

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Post #1360713

dean.giberson 64357

Posted Tuesday, September 18, 2012 5:58 AM

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Gotcha, not CHANGED just UPDATED.

Post #1360720

GilaMonster

Posted Tuesday, September 18, 2012 6:04 AM

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Yup. You want changed, you need to compare the columns in the inserted and deleted tables.

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
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Post #1360723

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