Good Day!

I need to change an update trigger in SQL Server 2008 to silently reject any attempts to change a single column value. The user may issue UPDATE statements which are updating numerous columns. I need to stop them from changing one column in particular, but I do not want to raise an error.

I tried using the deleted table to restore the original column value, but I cannot get it to work. Chances are I'd get a dangerous loop going, anyway. I also considered an INSTEAD OF trigger, but I'd that to be my last resort.

So, imagine I have this table:

TableA
ColumnUID   INTEGER PK
ColumnA     CHAR(10)
ColumnB    CHAR(100)

The user may issue this statement:
UPDATE TableA
SET ColumnA = 'ABC'
, ColumnB = 'Winter Park'
WHERE ColumnUID = 123;

I want the trigger to allow the ColumnB change to occur, but reject the change on ColumnA. It needs to be silent.

IF UPDATE(ColumnA)
BEGIN
    << Do not actually change ColumnA >>
END

Any assistance would be appreciated.