触发+变异错误+级联更新

Question

对于一个作业，我正在尝试使用Oracle SQL对其PK进行PK触发器的级联更新。我不能在FK中使用级联更新。

下面是我的代码，它会产生相应的错误：

CREATE or REPLACE trigger TR_PRODNO_FK_UPDATE
   /* trigger executes BEFORE
      an UPDATE of prodNo on the Product table */
   before update of prodNo on tbProduct
   /* trigger executes for each ROW */
   for each row

   /* begins a PL/SQL Block */
   begin
      /* update prodNo on tbProduct */
      UPDATE tbProduct a
         SET a.prodNo = :new.prodNo
         WHERE :old.prodNo = a.prodNo;
      /* update the prodNo on tbComponent */
      UPDATE tbComponent b
         SET b.prodNo = :new.prodNo
         WHERE :old.prodNo = b.prodNo;
      /* send message to output */
      dbms_output.put_line (
         '*** Related rows in the
            PRODUCT and COMPONENT table updated - TR_PRODNO_FK_UPDATE trigger');
   end TR_PRODNO_FK_UPDATE;
/

UPDATE tbProduct
    SET prodNo = '104'
    WHERE prodNo = '100';

enter image description here

这是怎么回事？有什么想法吗？