Question

我的问题如下，首先，这是我的代码，

ORA-04091: table SYSTEM.ISSUE is mutating, trigger/function may not see it
ORA-06512: at "SYSTEM.TRI_ISSUE", line 12
ORA-04088: error during execution of trigger 'SYSTEM.TRI_ISSUE'

我收到这样的错误，

{{1}}

我想要做的是，我想删除正在插入的行，通过＆＃39; After Insert＆＃39;触发，然后插入调用。我真的能这样做吗？谁能建议我一个补救措施？提前谢谢：）

Answer 1

有几种方法可以满足您的要求。

将所有逻辑放入程序中。这很可能是最好的方式。
将delete ISSUE where rollno = :new.rollno and accn_no = :new.accn_no;替换为raise_application_error(-20001, 'Book is not available!');

这样，用户就会收到异常并且未插入数据。
使用BEFORE STATEMENT，BEFORE EACH ROW和AFTER STATEMENT组件创建compound trigger。

创建视图和INSTEAD OF TRIGGER，就像这样：

CREATE OR REPLACE VIEW V_ISSUE AS 
SELECT * FROM ISSUE;

CREATE OR REPLACE TRIGGER tri_ISSUE
  INSTEAD OF INSERT OR DELETE ON V_ISSUE
  FOR EACH ROW

declare
    ct varchar2(20);
    cnt number(20);
begin
    if inserting
    then
        select bk_category into ct from BOOK_MASTER where accn_no=:new.accn_no;
        select available into cnt from BOOK_INFO where bk_category=ct;
        if(cnt=0)
        then
            dbms_output.put_line('Book is not available!');
            NULL; -- > do nothing
        else
            INSERT INTO ISSUE VALUES (... all coloums of this table);
            select bk_category into ct from BOOK_MASTER where accn_no=:new.accn_no;
            update BOOK_INFO set available=available-1 where bk_category=ct;
        end if;
    end if;
    if deleting
    then
        DELETE FROM ISSUE WHERE ...;
        select bk_category into ct from BOOK_MASTER where accn_no=:old.accn_no;
        update BOOK_INFO set available=available+1 where bk_category=ct;
    end if;
END;

如何通过触发器本身删除关于触发器被调用的行？

1 个答案: