SQL Trigger not working as expected - sql

Question

I have an SQL trigger as below
GO
create trigger ExpDateCheckCard
On Card
FOR Insert, Update
As
Declare #expDate as DateTime
Select #expDate = inserted.ExpirationDate from inserted
if (YEAR(#expDate) < 1971 )
BEGIN
UPdate Card set ExpirationDate = '1900-01-01 00:00:00' FROM Card, inserted
where inserted.RecordID = Card.RecordID
END
If i am right as per the trigger for every record inserted/updated when trigger runs it will check for the YEAR In the ExpirationDate column of that record and if the value is less than 1971 then it will update it with the date in the update query.
The weird thing is it is not working as expected.
The if condition does not seem to work.
Is anything wrong with this particular trigger.

Answer 1

YES - there's definitely something fundamentally wrong with the way you wrote this trigger.
SQL Server (assuming that's what you're using) will fire the trigger not once per row (as many folks including yourself) seem to think - the trigger is fired once per batch which might update or insert 10, 20, 50 rows at once.
Therefore, the Inserted pseudo table inside the trigger can (and will!) contain multiple rows - and in that case - what exactly does your statement here select?
Select #expDate = inserted.ExpirationDate from inserted
Either you'll just get one randon row (out of 50) and handle that (and ignore all 49 other rows), or you'll get an error....
You need to write your triggers with that in mind - you MUST always assume that Inserted (and Deleted) will contain multiple rows!
So you need to change your trigger to be something like:
CREATE TRIGGER ExpDateCheckCard
ON dbo.Card
FOR Insert, Update
AS
UPDATE dbo.Card
SET ExpirationDate = '1900-01-01 00:00:00'
FROM dbo.Card c
INNER JOIN inserted i ON i.RecordID = c.RecordID
WHERE YEAR(i.ExpirationDate) < 1971
(I've also changed your old-style JOIN syntax (comma-separated list of tables) to the ANSI standard that's been in place since 1992 - please do not use the comma-separated list of tables! Use proper ANSI JOINs. See this blog post for more background info: Bad habits to kick : using old-style JOINs)

Answer 2

try with this :
create trigger ExpDateCheckCard
On Card
FOR Insert, Update
As
BEGIN
Declare #expDate as DateTime
Select #expDate = inserted.ExpirationDate from inserted
if (YEAR(#expDate) < 1971 ) Begin
UPdate Card set ExpirationDate = '1900-01-01 00:00:00' FROM Card, inserted
where inserted.RecordID = Card.RecordID
end
END

Answer 3

You have to try this code
CREATE TRIGGER ExpDateCheckCard AFTER INSERT,Update ON Card
FOR EACH ROW
Declare #expDate as DateTime
Select #expDate = inserted.ExpirationDate from inserted
if (YEAR(#expDate) < 1971 )
BEGIN
update Card
set ExpirationDate = '1900-01-01 00:00:00' FROM Card, inserted
where inserted.RecordID = Card.RecordID
END