Update Trigger on a Table [closed]

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If a Table A is updated a trigger gets fired. That trigger calls another SP to do some processing. Is there any chance that if SP fails the update that happened on Table A will be reverted?

I have a code just after the update "If Sqlca.SqlCode" and this always has 0 coming for the update.

Please Help!!

Answer 1

Triggers can do things AFTER the DML is executed, INSTEAD OF executing the DML, etc. So yes, there is a chance that the update (dml) wont happen if the SP fails -- just depends on how you write it / what features you use.

Read up on triggers a bit here: http://technet.microsoft.com/en-us/library/ms189799%28v=sql.105%29.aspx

If you want a more specific answer for trigger in quesiton, then you'll need to post the code.

Answer 2

Yes, if the trigger encounters an error (internally or through calling some external procedure) and rolls back the transaction, it will roll back the whole transaction, including whatever UPDATE caused the trigger to fire in the first place. There are multiple ways to get around this, if it is not the behavior you want:

• use TRY / CATCH to absorb any errors form the external procedure, or move the procedure logic into the trigger, or add proper error handling to the stored procedure so that, if you don't care that an error happened there, it doesn't bubble up and roll back everything.

• use an INSTEAD OF trigger - combined with TRY / CATCH (or possibly committing your own UPDATE first), you should be able to update the table without caring whether the external stored procedure fails.

Example of the INSTEAD OF trigger:

USE tempdb;
GO

CREATE TABLE dbo.flooblat(id INT PRIMARY KEY, name VARCHAR(32));
INSERT dbo.flooblat(id,name) VALUES(1, 'Bob');
GO

CREATE PROCEDURE dbo.oh_my
AS
  SELECT 1/0;
GO

CREATE TRIGGER dbo.trFlooblat
  ON dbo.flooblat
  INSTEAD OF UPDATE
AS
BEGIN
  SET NOCOUNT ON;

  UPDATE f SET f.name = i.name
    FROM dbo.flooblat AS f
    INNER JOIN inserted AS i
    ON f.id = i.id;

  COMMIT TRANSACTION;

  EXEC dbo.oh_my;
END
GO

UPDATE dbo.flooblat SET name = 'Frank';
GO

SELECT id, name FROM dbo.flooblat;
GO

Results:

Msg 8134, Level 16, State 1, Procedure oh_my
Divide by zero error encountered.
The statement has been terminated.

However, the SELECT reveals that, even though an error occurred in the trigger, it happened after the UPDATE was committed - so unlike an exception that occurs in an AFTER trigger (without proper error handling), we were able to prevent the error from rolling back all of the work we've done.

id    name
----  -----
1     Frank