In a trigger, how to check if no fields have changed?

Question

If we receive an update statement that does not check if the value has changed in the where clause, what are the different ways to ignore that update inside a trigger?

I know we can do a comparison of each individual field (handling the ISNULL side as well), but where it's a table that has 50+ fields, is there a faster/easier way to do it?

Note: This could be used to reduce IO/noise in audit records etc...

EXAMPLE

For a table of:

CREATE TABLE myTest
(ID int NOT NULL IDENTITY(1,1), 
 Field1 varchar(10) NULL,
 Field2 varchar(20) NULL)

with an after updater trigger containing:

INSERT INTO myTestAudit (ID, Field1, Field2, DateTimeUpdate)
SELECT ID, Field1, Field2, getDate()
FROM inserted

with initial values:

INSERT INTO myTest (Field1, Field2)
SELECT 'a', 'b' UNION ALL
SELECT 'a', 'c'

Now run an update:

UPDATE myTest set Field2 = 'b' WHERE Field1 = 'a'

Answer 1

To bring back rows where at least one value has changed you can use

SELECT /*TODO: Column List*/
FROM   INSERTED I
       JOIN DELETED D
         ON I.ID = D.ID
            AND EXISTS (SELECT I.*
                        EXCEPT
                        SELECT D.*)  

Answer 2

Put this as the very first line in your trigger:

-- Exit trigger if no data was actually modified
IF (@@ROWCOUNT  = 0)  return

I do this in all of my audit triggers. It is short and to the point, definitely cuts down on wasted I/O.

Update: Sorry, I misread your question. I thought you asked how to exit the trigger if no data has changed.