oracle判断监控某字段值变动的 trigger

TRIGGER Z_M_QY_RY_Update BEFORE UPDATE   ON Z_M_QY_RY                      FOR EACH ROW                        begin                      IF UPDATING('RYNAME') THEN                  BEGIN                     IF NVL(TO_CHAR(:new.RYNAME),'^') != NVL(TO_CHAR(:old.RYNAME),'^') THEN                    BEGIN                       insert into z_m_log(tablename,colname,bgnr,rid,pk,EDIT_USER) values('Z_M_QY_RY','人员姓名','【'||NVL((:old.RYNAME),'')||'】-->【'||NVL((:new.RYNAME),'')||'】',:new.rowid,:new.ID,:new.EDIT_USER);                     END;                     END IF;                   END;