sql - 触发以防止从表中删除任何内容

Question

此新租赁历史记录表的触发器，可防止从表中删除。

CREATE OR REPLACE  TRIGGER RENTALHIS_DEL
BEFORE DELETE ON RENTALHISTORY
BEGIN
dbms_output.put_line( 'Records can not be deleted');
END;

DELETE FROM RENTALHISTORY WHERE RENTALID = 1;



-- It is deleting before it says it can not delete

1 rows deleted.

Records can not be deleted

Answer 1

dbms_output.put_line( 'Records can not be deleted');

以上只是打印文本和触发器成功完成，然后删除仍然发生。您想要做的是引发错误以阻止程序完成。

使用标准程序 raise_application_error停止程序并引发错误:

CREATE OR REPLACE  TRIGGER RENTALHIS_DEL
BEFORE DELETE ON RENTALHISTORY
BEGIN
    raise_application_error(-20001,'Records can not be deleted');
END;
/