Can update triggers detect the column in the update statement?

[Ben Chobot <bench@xxxxxxxxxxxxxxx>]

Say I have:

create t (c1 int not null, c2 int);

Is it possible to create an update trigger on t such updates will only  
be allowed if the update statement explicitly sets c1, even if the new  
value is the same?


(I'm trying to write a change log system where the users are  
application users, not database users.)