更新时出现变异触发错误

Question

当colB发生变化时，我正在尝试更新lastupdate列，但是当我在触发器下面使用时，我得到了变异触发器错误，因此我也尝试使用复合触发器

 create or replace trigger LASTUPDATE_TRIG
 BEFORE update on TABLE_A

 referencing OLD as old NEW as new
 for each row WHEN (new.colB <> old.COLB)
 DECLARE

V_NUMBER NUMBER;
begin

V_NUMBER := :new.COLA;
update TABLE set LAST_UPDATE_DATE = sysdate where colA= v_number;
end; 

Answer 1

          CREATE OR REPLACE TRIGGER LASTUPDATE_TRIG
    before INSERT OR DELETE OR UPDATE ON FQC_TABLE A
 referencing old as old new as new 
    for  each row 

    begin

        if :new.COLB <> :old.COLB and updating  then
         :new.LAST_UPDATE_DATE:=sysdate;
        end if;

end;