INSERT trigger to update a field that is NOT NULL in the same table

Question

I have a situation where I need to merge two product tables into one and need to keep both id fields. The Id field is the pk and an identity column. On insert I want to update the prodId to match the Id of the newly inserted row. This is what I have but I get an error saying that I cannot insert null into ProductId. What am I doing wrong?

ALTER TRIGGER SyncId
    ON Product
FOR INSERT
AS
BEGIN
    DECLARE @ID INT
    SET @ID = (SELECT ID FROM Inserted)
    UPDATE Product SET
        ProdId = @ID
    WHERE
        Id = @ID    
END

Answer 1

You could create an INSTEAD OF trigger for the INSERT . You would then have to recreate the actual INSERT logic. You might need a view of the table for the trigger to sit on though... I don't recall if an INSERT within the trigger will work or not and can't test it right now.

Also, your trigger as written will only work if a single row is being updated. You should always write your triggers to be able to handle multiple rows in the INSERTED and DELETED tables.