Trigger after insert on not null column - sql

Question

I have a table that contains two not null columns Created and Updated.
I wrote corresponding triggers
ALTER TRIGGER [dbo].[tr_category_inserted] ON [dbo].[Category]
AFTER INSERT
AS
BEGIN
UPDATE Category
SET Created = GETDATE(), Updated = GETDATE()
FROM inserted
WHERE Category.ID = inserted.ID;
END
and
ALTER TRIGGER [dbo].[tr_category_updated] ON [dbo].[Category]
AFTER UPDATE
AS
BEGIN
UPDATE Category
SET Updated = GETDATE()
FROM inserted
inner join [dbo].[Category] c on c.ID = inserted.ID
END
but if I am inserting a new row I get an error
Cannot insert the value NULL into column 'Created', table
'Category'; column does not allow nulls. INSERT fails.
Insert command:
INSERT INTO [Category]([Name], [ShowInMenu], [Deleted])
VALUES ('category1', 0, 0)
How can I write such triggers without a setting to these columns to allow null?

Answer 1

Modify your table like this:
ALTER TABLE yourTable MODIFY COLUMN updated timestamp DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;
ALTER TABLE yourTable MODIFY COLUMN created timestamp DEFAULT 0;
Set the default for the created to column to 0. Unfortunately MySQL does not allow two timestamp columns with default CURRENT_TIMESTAMP in one table. To overcome this you just have to insert a NULL value into created column and you will have both columns to the current timestamp.
INSERT INTO yourTable (col1, created) VALUES ('whatever', NULL);
Or you set the default to a valid timestamp like
ALTER TABLE yourTable MODIFY COLUMN created timestamp DEFAULT '1970-01-01 00:00:00';
and modify your trigger like this:
ALTER TRIGGER [dbo].[tr_category_inserted] ON [dbo].[Category]
AFTER INSERT
AS
BEGIN
UPDATE Category
SET Created = GETDATE()
/* FROM inserted */ /*don't know where you got that from, do you port from SQL Server?*/
WHERE Category.ID = NEW.ID;
END

Answer 2

Error occurring because trigger works after insertion only, and you may not be inserting the column values Created and Updated at the time of insert.
So for eliminating the error, you can insert/populate the columns Created and Updated along with insert.
OR
You can add default value property of column. Please check the links for details
Add column, with default value, to existing table in SQL Server
Specify Default Values for Columns

Answer 3

Possible use INSTEAD OF trigger
CREATE TRIGGER [dbo].[tr_category_inserted] ON [dbo].[Category]
INSTEAD OF INSERT
AS
BEGIN
INSERT Category(Name, ShowInMenu, Deleted, Created, Updated)
SELECT Name, ShowInMenu, Deleted, GETDATE(), GETDATE()
FROM inserted i
END

Answer 4

I typically allow the last updated column to be null since I want to know if its never been altered. If you must keep both fields nullable I would add a default value to those columns like this:
ALTER TABLE [dbo].[Category] ADD DEFAULT (getdate()) FOR [Created]
GO
ALTER TABLE [dbo].[Category] ADD DEFAULT (getdate()) FOR [LastUpdated]
GO
Then you won't need the trigger for the insert.
If you really want to use a trigger anyway you will have to specify INSTEAD OF rather than AFTER and include the insert statement.