-- See a trigger say that it didn't fire....
--  (actually, the trigger fires, but internally it sees 
--   that the tested field VALUE wasn't affected)
CREATE TABLE TriggerTest (Value int, Text char(10))
GO
INSERT INTO TriggerTest VALUES (1, 'Hello')
GO

CREATE TRIGGER tr_TriggerTest
   ON TriggerTest 
  AFTER UPDATE
 AS BEGIN   SET NOCOUNT ON;
   IF UPDATE(Value) 
     PRINT 'The trigger fired'
   ELSE 
     PRINT 'The trigger did not fire'
END
GO
UPDATE TriggerTest SET Text = Text

--See trigger fire with 0 rows affected
UPDATE TriggerTest SET Value = Value
where value = 7

--See an error prevent the update and thereby the trigger
UPDATE TriggerTest SET Value = 'Value'