Trigger to fire only if a condition is met in SQL Server

Question

I hope this is a simple enough question for any SQL people out there...

We have a table which hold system configuration data, and this is tied to a history table via triggers so we can track who changed what, and when.

I have a requirement to add another value in to this table, but it is one that will change frequently from code, and has a requirement that we don't track it's history (we don't want to clog the table with many thousands of updates per day.

At present, our trigger is a little like this...

CREATE TRIGGER      [dbo].[SystemParameterInsertUpdate] ON      [dbo].[SystemParameter] FOR INSERT, UPDATE  AS   BEGIN     SET NOCOUNT ON       INSERT INTO SystemParameterHistory        (         Attribute,         ParameterValue,         ParameterDescription,         ChangeDate       )     SELECT       Attribute,       ParameterValue,       ParameterDescription,       ChangeDate     FROM Inserted AS I END 

I'd like to be able to add some logic to stop it creating the record if an Attribute colum value is prefixed with a specific string (e.g. "NoHist_")

Given that I have almost no experience working with triggers, I was wondering how it would be best to implement this... I have tried a where clause like the following

where I.Attribute NOT LIKE 'NoHist_%' 

but it doesn't seem to work. The value is still copied over into the history table.

Any help you could offer would be appreciated.

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OK - as predicted by Cade Roux, this fail spectacularly on multiple updates. I'm going to have to take a new approach to this. Does anyone have any other suggestions, please?

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Guys - Please educate me here... Why would LEFT() be preferable to LIKE in this scenario? I know I've accepted the answer, but I'd like to know for my own education.

Answer 1

Given that a WHERE clause did not work, maybe this will:

CREATE TRIGGER      [dbo].[SystemParameterInsertUpdate] ON      [dbo].[SystemParameter] FOR INSERT, UPDATE  AS   BEGIN     SET NOCOUNT ON        If (SELECT Attribute FROM INSERTED) LIKE 'NoHist_%'       Begin           Return       End        INSERT INTO SystemParameterHistory        (         Attribute,         ParameterValue,         ParameterDescription,         ChangeDate       )     SELECT       Attribute,       ParameterValue,       ParameterDescription,       ChangeDate     FROM Inserted AS I END 

Answer 2

How about this?

CREATE TRIGGER  [dbo].[SystemParameterInsertUpdate] ON  [dbo].[SystemParameter] FOR INSERT, UPDATE  AS BEGIN SET NOCOUNT ON   IF (LEFT((SELECT Attribute FROM INSERTED), 7) <> 'NoHist_')    BEGIN       INSERT INTO SystemParameterHistory        (         Attribute,         ParameterValue,         ParameterDescription,         ChangeDate       )     SELECT       Attribute,       ParameterValue,       ParameterDescription,       ChangeDate    FROM Inserted AS I END END