Trigger for only changed values

You need this:

In an UPDATE trigger, a column name can be specified with an UPDATING conditional predicate to determine if the named column is being updated. For example, assume a trigger is defined as the following:

CREATE OR REPLACE TRIGGER ...
... UPDATE OF Sal, Comm ON Emp_tab ...
BEGIN

... IF UPDATING ('SAL') THEN ... END IF;

END;

From Oracle documentation(9i)

11gR2 documentation

Trigger for only changed values.

As an example (only NOT NULL support) (comparison operators with NULL always return FALSE):

CREATE OR REPLACE TRIGGER trigger_department_update
  BEFORE UPDATE OF 
      department_id,
      cluster_id, 
      division_id, 
      macroregion_id, 
      address, 
      email
    ON cl_department
  FOR EACH ROW
BEGIN
  IF (
    :new.department_id != :old.department_id
    OR :new.cluster_id != :old.cluster_id
    OR :new.division_id != :old.division_id
    OR :new.macroregion_id != :old.macroregion_id
    OR :new.address != :old.address
    OR :new.email != :old.email
  ) 
    THEN :new.update_date := CURRENT_TIMESTAMP; 
  END IF;
END;

With NULL support (Thanks to @Oleg in the comments below this post) (Thanks to @Chris Bandy for the answer):

CREATE OR REPLACE TRIGGER trigger_department_update
  BEFORE UPDATE OF 
      department_id,
      cluster_id, 
      division_id, 
      macroregion_id, 
      address, 
      email
    ON cl_department
  FOR EACH ROW
BEGIN
  IF (
    ((:new.department_id <> :old.department_id OR :new.department_id IS NULL OR :old.department_id IS NULL) AND NOT (:new.department_id IS NULL AND :old.department_id IS NULL))
    OR ((:new.cluster_id <> :old.cluster_id OR :new.cluster_id IS NULL OR :old.cluster_id IS NULL) AND NOT (:new.cluster_id IS NULL AND :old.cluster_id IS NULL))
    OR ((:new.division_id <> :old.division_id OR :new.division_id IS NULL OR :old.division_id IS NULL) AND NOT (:new.division_id IS NULL AND :old.division_id IS NULL))
    OR ((:new.macroregion_id <> :old.macroregion_id OR :new.macroregion_id IS NULL OR :old.macroregion_id IS NULL) AND NOT (:new.macroregion_id IS NULL AND :old.macroregion_id IS NULL))
    OR ((:new.address <> :old.address OR :new.address IS NULL OR :old.address IS NULL) AND NOT (:new.address IS NULL AND :old.address IS NULL))
    OR ((:new.email <> :old.email OR :new.email IS NULL OR :old.email IS NULL) AND NOT (:new.email IS NULL AND :old.email IS NULL))
  ) 
    THEN :new.update_date := CURRENT_TIMESTAMP; 
  END IF;
END;