How can I edit values of an INSERT in a trigger on SQL Server?

Question

I have the table Tb

ID | Name   | Desc
-------------------------
 1 | Sample | sample desc

I want to create a trigger on INSERT that will change the value of the inserting Desc, for example:

INSERT INTO Tb(Name, Desc) VALUES ('x', 'y')

Will result in

ID | Name   | Desc
-------------------------
 1 | Sample | sample desc
 2 | x      | Y edited

In the above example I got the value of the inserting Desc changed it to uppercase and added edited on the end.

That's what I need, get the Desc that is being inserted and modify it.

How can I do that?

Is it better to handle it after the insert with an update? Or make a trigger with INSTEAD OF INSERT and modify it everytime the table structure changes?

Answer 1

Use an after insert trigger. Join from the inserted pseudo table to Tb on the primary key. Then update the values of desc. Something like: (But may not compile)

CREATE TRIGGER TbFixTb_Trg 
ON  Tb  
AFTER INSERT 
AS  
BEGIN 
    UPDATE Tb
    SET DESC = SomeTransformationOf(i.DESC)
    FROM Tb
    INNER JOIN inserted i on i.Id = Tb.Id
END  
GO

This trigger happens after the insert has happened, but before insert statement completes. So the new, incorrect values are already placed in the target table. This trigger will not need to change as columns are added, deleted, etc.

Caveat Integrity constraints are enforced before the after trigger fires. So you can't put on a check constraint to enforce the proper form of DESC. Because that would cause the statement to fail prior to the trigger having a chance to fix anything. (Please double check this paragraph before relying on it. It's been awhile since I've written a trigger.)