Trigger that will not fire when certain column is updated

I'm trying to write an Oracle update trigger that will NOT fire when a certain column is updated. Let's say I have four columns, a, b, c and d. I only want the trigger to work when a, b and d are updated. It would be best if I could say something like "update on table when column not like c." The c column is consistent throughout all of my 196 tables; the columns a,b and d are not. I'm using Oracle 8.1.7.

In Oracle, a trigger can be fired on UPDATE of specific columns. The following syntax can be used to define a trigger that will fire on updates of only specific columns of a table:

CREATE OR REPLACE TRIGGER my_tab_upd_trigger
BEFORE UPDATE OF column_a,column_b,column_d
ON my_tab
FOR EACH ROW
BEGIN
....
END;
/

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