SQL SERVER – Create TSQL Trigger to add date to existing record after INSERT or UPDATE

I came across an interesting issue with a web application I have been trying to create. DEFAULTS in SQL Server didn’t seem to be registering when new records were inserted through the web application.

How come? Surely the web application is not bypassing requirements set out by the database.

What I believe is happening is that the web application is explicitly supplying a null value to the dateupdated field and because of this the default value is NOT applied by SQL Server. You are therefore in the strange position of creating a trigger on a column after insert. Normally you would never really do this as that’s specifically what default is for.

Here’s code to create the trigger on the SQL Server that will do just this.

CREATE TRIGGER TR_moddate
On T0001PersonData
AFTER INSERT, UPDATE
AS
BEGIN
UPDATE T0001PersonData SET DATEUPDATED=GETDATE()
WHERE PKID IN (SELECT PKID FROM INSERTED)
END

Some explanation – This updates the field DateUpdated within the table T0001PersonData after an update or an insert. If you have default on a column this may mean that it updates to default then to null then to trigger so you may wish to remove the default on the column. Alternatively you may wish to get the front end to update to the current date. I guess this could have performance issues at scale but my application is pretty small beer so I am happy with this at the moment. I think I prefer to have it at database level as well. It should be noted that INSERTED is actually a ALIAS table created by SQL Server and held in memory that allows for reference to pull out items before they are registered in the database. Leaving out the where clause may have resulted in the application updating the dateupdated column for all records anytime an update or insert was performed. BE WARNED

About Mark

Mark Brooks a forty something individual working and living in and around Edinburgh
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